Complete Guide To HTML Compiled by Matthew Probert Disclaimer This document is supplied in good faith, however no responsibility can be accepted for the accuracy of the information contained herein or any loss or damage resulting from any advice given or implied by the author. This document mentions several HTML viewers and companies by name, this is not intended as an endorsment of any company or product. All trademarks are recognised as belonging to their respective owners. Introduction First people communicated ideas through hand signals and voice, then drawings on cave walls then through hand painted manuscripts and later printed paper books and leaflets. With the advent of the computer came the facility to publish documents not on paper, but electronicaly instead. The computer screen displaying the document, rather than it being laid out on a leaf of paper. Publishing information electronicaly requires some medium to present the information to the reader. A graphics viewer is used to access pictures, for example. An HTML viewer (or web browser as they are commonly known) is a program which presents electronic documents, in HTML format, to the reader. The HyperText Mark-up Language (HTML) is a simple data format used to create formatted electronic documents with hyperlinks to other documents and resources (this hyperlinking to other documents is known as hypertext) that are portable from one computer platform to another. That is, an HTML document created on a PC may also be read by a user of a UNIX machine or an Atari, Macintosh and so on. The term "mark-up" is a printing expression describing the process of putting together words and picture to form a document. HTML, is used electronically to put together words (text) and pictures (images) into a finished presentation document. Recent inovations mean that video clips and sound can also be added, making HTML a full multimedia publishing medium. You will probably be familiar with the idea of formatted documents, these are produced by word processors. A formatted document has a variation in its appearance. It looks pretty. Where as an unformatted document has all the text in one style. Links to other documents and resources may be a newer idea for you. A standard formatted document simply conveys information, and may suggest other sources of information to the reader. A hypertext document does the same, but where a suggestion of other information is made a provision is made for the reader to click the mouse button or press a keyboard button and the program being used to view the hypertext document will load and display the linked document. For example, this is a formatted text document that you are reading. If I wish to refer you to another document, titled "order.doc" to view that document you need to select the file option from your viewer software, and open the named file. With a hypertext document, you could simply point the mouse to the words "order.doc" which would be displayed in a different colour, and click the mouse button to ask the viewer software to load and display the document. Of course as the author of the document, I would have to include some instruction to the viewer software that would enable you to do that. These instructions form part of the HTML language. They are called "hyperlinks" and provide a path to other documents or resources, called Uniform Resource Locations, or URLs for short. HTML documents are viewed with an HTML viewer, or "web browser" as they are starting to be known in PC circles. The most common HTML viewers used by PC users are Microsoft's Internet Explorer and Netscape's Navigator. But there are others. Mosaic, by NCSA is available in a number of custom Internet packages including Quarter- deck's Internet connectivity package and is perhaps the next most widely used. What is less well known is that all HTML viewers present HTML documents slightly differently. Although HTML is specified, HTML viewers do not pay too much attention to the official specifications and manufacturers have added support (both documented and not!) for a variety of additional features and commands including built-in Java compilers to understand Java code and support for Frames. If you are publishing your document for a known audience, you should know which HTML viewer will be used to access the document, and you should be aware of the facilities supported by that viewer. When publishing for the World Wide Web you should remember that your audience is comprised of millions of people, with dozens of different HTML viewers, which whilst supporting basic features, have many discrepancies in their support of advanced features. Some may not even have the ability to display images. So while this e-text describes and illustrates many features found only in one or two HTML viewers, it should not be viewed as a recommendation to use these features for general HTML publishing. Basic Concepts As with any aspect of computing, HTML introduces some new concepts and jargon. It is necessary to be familiar with these basic terms in order to understand the rest of this document. Tags: Tags provide instructions to an HTML viewer about elements such as headings, paragraphs, lists, character highlighting, and hyperlinks. Most HTML elements are identified in a document as a start-tag followed by an end tag. The start-tag provides the HTML viewer with the element name and attributes, followed by the content. The end-tag tells the HTML viewer about the end of the element. Start-tags are delimited by `<'and `>'; end tags are delimited by `</' and `>'. For example: <H1>This is a Heading</H1> In the above example the start-tag is <H1> and the end-tag is </H1> Comments: To include comments in an HTML document, use a comment declaration. A comment declaration consists of `<!' followed by zero or more comments followed by `>'. Each comment starts with `_`and includes all text up to and including the next occurrence of `_`. In a comment declaration, white space is allowed after each comment, but not before the first comment. The entire comment declaration is ignored. For example: <!-- This is a comment --> <!-- This is a multiple-line comment --> Head: The head of an HTML document, defined by the start-tag <HEAD> and delimited by the end-tag </HEAD>, is where heading information about the document goes. The heading information is an unordered collection of information about the document, such as the title of the document. For example: <HEAD> <TITLE>Document Title</TITLE> </HEAD> This example declares the document title to the HTML viewer as "Document Title". The title element contains your document title and identifies its content in a global context. The title is displayed somewhere on the HTML viewer window (usually at the top), but not within the document area. The title is also used for bookmarking and during a WAIS search of a server and should be less than 64 characters long. Title: Every HTML document must contain a TITLE element. The title should identify the contents of the document in a global context. A short title, such as "Introduction" may be meaningless out of context. A title such as "Introduction to HTML Elements" is more appropriate. An HTML viewer may display the title of a document in a history list or as a label for the window displaying the document. Body: The BODY section of an HTML document is where the text to be displayed is placed. This is the largest section of an HTML document, and is defined by the start-tag <BODY> and terminated by the end-tag </BODY> For example: <BODY> This is displayed in the HTML viewer text window </BODY> Headings: Headings are generally displayed in a larger type-face (or font) than the main text. HTML provides two systems for declaring a heading. The old system, which is recognised by all HTML viewers, supports six sizes of text declared by the start-tags <H1>, <H2>, <H3>, <H4>, <H5> and <H6>, each of which has a corresponding end-tag such as </H1>, </H2> and so on. The text sizes range from <H1> the biggest, through <H3> the default size to <H6> the smallest. For example: <H1>This is a large heading</H1> <H3>This is in the normal default size</H3> <H6>This is very small!</H6> Paragraphs: Unlike most word processors, HTML viewers ignore carriage returns, and additionally multiple spaces are reduced to a single space. The paragraph command (<P> and </P>) tells the HTML viewer that the text contained within the start-tag and end-tag is a paragraph. Paragraphs are displayed by the HTML viewer separated by a single blank line from the preceding items. For example: <P> This is a paragraph. This second line is actually displayed by an HTML viewer on the same line as the previous line, as the carriage return is ignored. </P> <P> This second paragraph is displayed with a single blank line between it and the previous paragraph. </P> This results in the following to be displayed by an HTML viewer: This is a paragraph. This second line is actually displayed by an HTML viewer on the same line as the previous line, as the carriage return is ignored. This second paragraph is displayed with a single blank line between it and the previous paragraph. Alignment: Text and images may be aligned to the left, to the right or centred. For example: Left alignment Right alignment Center alignment Lists: A list is simply a list of items. The HTML viewer automatically starts each list item on a new line, and handles list numbering and bulleting depending upon how the HTML author has declared the list. Base URL: The Base URL gives the HTML viewer a point of reference for hyperlinks. Usually the base URL is not specified, and is taken as the URL address of the current document. Hyperlinks: Hyperlinks are a provision allowing the user of the HTML document to navigate through the document and to external resources. Hyperlinks may be local, allowing navigation within the currently loaded document, or external providing access to other documents not loaded and resources such as ftp servers and mail servers. Navigation through hyperlinks usually occurs by positioning the pointer over the link with the mouse, and then pressing the left mouse button. The hyperlink may be displayed to the user either as text, in which case it will normally be displayed in a distinctive colour and underlined, or as an image. In both cases, when the pointer passes onto a hyperlink it will change shape indicating a selectable hyperlink. Meta: The META element is an extensible container for use in identifying specialized document meta-information. Meta-information has two main functions: 1) to provide a means to discover that the data set exists and how it might be obtained or accessed; and 2) to document the content, quality, and features of a data set, indicating its fitness for use. Each META element specifies a name/value pair. If multiple META elements are provided with the same name, their combined contents - concatenated as a comma-separated list - is the value associated with that name. HTTP servers may read the content of the document HEAD to generate header fields from certain Meta information. WWW Search Engines also may make use of META information to automatically build an entry for a site. Forms: Forms provide a mechanism for passing information from the HTML viewer back to a program at the web server or through email to you. A Basic HTML Document A simple HTML document is comprised of the following components: An HTML declaration tag: <HTML> A heading tag: <HEAD> A title, such as: <TITLE>Title text</TITLE> A body declaration tag: <BODY> The main body of the document. A body termination tag </BODY> and finally an HTML termination tag: </HTML> For example: <HTML> <HEAD> <TITLE>Example HTML Document</TITLE> <BODY> This is an example HTML document. </BODY> </HTML> Adding Headings: Headings can be added to an HTML document with the heading tags; <H1> through <H6>. An example HTML document using a heading: <HTML> <HEAD> <TITLE>Example HTML Document</TITLE> <BODY> <H1>Main Heading</H1> <P> This is an example HTML document. </P> </BODY> Notice the use of the paragraph start-tag <P> and end-tag </P> which tells the HTML viewer to display the text as a new paragraph, and not as a continuation of the heading line. Newer HTML viewers, such as Netscape Navigator and Microsoft Internet Explorer aslo support more advanced formatting for headings and other text, but this will be covered later. Simple Formatting HTML viewers do not recognise carriage-returns in the text. Instead, they display the text as continuous lines, breaking each line at a word end so that it fits in the text window. This is known as word- wrap. You can force a line break with the HTML tag <BR>. For example: This is line one<BR>This is line two Which displays as: This is line one This is line two Blank lines can be inserted by using multiple occurrences of the <BR> tag, thus: This is line one<BR><BR>This is line two Which displays as: This is line one This is line two When text flows around a figure or table in the margin, you sometimes want to start an element like a header, paragraph or list below the figure rather than alongside it. The CLEAR command allows you to move down unconditionally: CLEAR=LEFT move down until left margin is clear CLEAR=RIGHT move down until right margin is clear CLEAR=ALL move down until both margins are clear Alternatively, you can decide to place the element alongside the figure just so long as there is enough room. The minimum width needed is specified as: CLEAR="100 pixels" move down until there is at least 100 pixels free For example: <BR CLEAR=LEFT> Centring a line of text is also easy. The HTML tag <CENTER> causes all subsequent text and images to be displayed in the centre of the text window until a </CENTER> end-tag is reached. For example: <HTML> <HEAD> <TITLE>Example HTML Document</TITLE> <BODY> <CENTER> <H1>Main Heading</H1> </CENTER> <P> This is an example HTML document. </P> </BODY> If you just want to centre a single heading, you can use the "align=" command within the heading tag, for example: <H1 align=center> The example HTML document would then look like this: <HTML> <HEAD> <TITLE>Example HTML Document</TITLE> <BODY> <H1 align=center>Main Heading</H1> <P> This is an example HTML document. </P> </BODY> This will display as: Main Heading This is an example HTML document. The ALIGN= command may also be added to the paragraph tag, <P> to align an entire paragraph, for example: <P ALIGN=CENTER> In addition to defining the size of the typeface used to display text (heading), HTML also supports bold, italic, strikethrough, underline, subscript and superscript formats. The following example illustrates the popular formatting tags: <HTML> <HEAD> <TITLE>Example HTML Document</TITLE> <BODY> <H1 align=center>Main Heading</H1> <P> This is an example HTML document illustrating some basic text formatting tags. <P> <B>Bold</B> <P> <I>Italic</I> <P> <SUB>Subscript</SUB> <P> <U>Underline</U> <P> <SUP>Superscript</SUP> <P> <STRIKE>Strikeout</STRIKE> <P> <TT>Typewriter (fixed width font)</TT> <P> <PRE>Preformatted (used for displaying source code etc.)</PRE> </BODY> Formatting tags may also be nested to create multiple effects such as BOLD ITALIC, for example: <B><I>This is Bold Italic</I></B> But you must remember to end-tag in the reverse order to the start- tags to keep the nesting correct. Blockquote: Text defined as a "blockquote" is displayed as a new paragraph, and usually displayed indented from the left margin, and with some HTML viewers in a unique typeface. A blockquote is declared by the tag pair <BLOCKQUOTE> and </BLOCKQUOTE>, for example: <BLOCKQUOTE> This text will normally be displayed indented, and if viewed with Mosaic, displayed in a unique font type face. </BLOCKQUOTE> Address: Text defined as an "address block" is displayed as a new paragraph and usually in italic. An address is declared by the tag pair <ADDRESS > and </ADDRESS >, for example: <ADDRESS> This text will normally be displayed in italic. </ADDRESS> Emphasis: Emphasised text is declared by the tag pair <EM> and </EM> and is usually displayed in italic. Strong: Strong text is declared by the tag pair <STRONG> and </STRONG> and is usually displayed in bold. Citation: Citation text is declared by the tag pair <CITE> and </CITE> and is usually displayed in italic. Source Code: Source code is declared by the tag pair <CODE> and </CODE> and is usually displayed in a fixed width font, though this may be changed by the user of the HTML viewer. Sample Output: Sample Output is declared by the tag pair <SAMP> and </SAMP> and is usually displayed in a fixed width font, though some HTML viewers (notably Mosaic) allow the user to change this. Keyboard Input: "Keyboard Input" is declared by the tag pair <KBD> and </KBD> and is usually displayed in a different font face and style to the ordinary text. Variable: Variable text is declared by the tag pair <VAR> and </VAR> and is usually displayed in either a fixed width font or an italic font to emphasis it. Big: Big text is declared by the tag pair <BIG> and </BIG> and is usually displayed larger than the ordinary text, but without the new line which accompanies a heading <Hn> tag. Small: Small text is declared by the tag pair <SMALL> and </SMALL> and is usually displayed smaller than the ordinary text, but without the new line which accompanies a heading <Hn> tag. Dividers HTML provides three basic ways of dividing a document window: Paragraphs, Line Breaks, and Horizontal Rules. Paragraphs are contained within a <P> and </P> tag pair, although the end-tag </P> is not needed if another paragraph starts with a <P> start-tag. Paragraphs may be aligned, with the "align=" command, for example: <P> A standard paragraph <P align=center> Center aligned paragraph <P align=left> Left aligned paragraph <P align=right> Right aligned paragraph Line breaks are enforced with the <BR> tag. When an HTML viewer encounters the <BR> tag, the cursor is moved down one line and to the left of the window. If an alignment is in operation, the next displayed line will be aligned correctly. Horizontal rules are affected with the <HR> tag. This tells the HTML viewer to display a graphical horizontal line across the entire width of the window. The form of the rule can be amended with the optional "size=", "width=", "noshade" and "align=" parameters. The vertical thickness of the horizontal rule can be defined by adding a size= parameter to the <HR> tag. The number following the size= parameter tells the HTML viewer how many vertical pixel lines to use for the rule. For example: <HR size=4> By default, a horizontal rule extends the entire width of the window. The width= parameter may be used to specify the horizontal width of the rule either in pixels, or as a percentage of the window width: <HR width=100> <HR width=50%> Horizontal rules are usually aligned in the centre of the window, or if an alignment is in force, they follow the rules of the current alignment. This may be overridden by the align= parameter, for example: <HR align=left> <HR align=center> <HR align=right> Finally, horizontal rules are displayed in a 3d representation. This can be changed to a solid thick 2 dimensional line with the noshade parameter: <HR noshade> As usual, these parameters can be mixed together, for example: <HR align=right width=50% size=10 noshade> Images Most newer HTML viewers can display pictures, called images, in various forms. The most popular being GIF and JPEG formats. The procedure for telling the HTML viewer to display the image is the same regardless of the image format: <img src="imagename"> For example: <img src="picture.gif"> Will cause the HTML viewer to display the image "picture.gif". Some HTML viewers cannot display images, so you can provide text which will be displayed by these viewers instead of the image by including it with the "alt=" parameter, for example: <img src="picture.gif" alt="Picture of a tree"> The image may be aligned in relation to the surrounding text using the optional "align=" parameter. If no alignment parameter is specified, text following the image will be displayed at the bottom right of the image. Different HTML viewers handle the alignment of text and images differently, so be careful! The size of the image can be declared to the HTML viewer with the optional "width=" and "height=" parameters. If these are not specified, the HTML viewer will display the image at its full size. If however you specify these size parameters, the image will be displayed to the specified size in pixels. For example: <img src="picture.gif" width=640 height=480> Lists HTML supports a number of types of list: Ordered, Unordered, Definition, Menu and Directory. Ordered lists are displayed one item per line, with a sequential numbering system to the left of each item. An ordered list is declared by the start-tag <OL> and terminated with the end-tag </OL>. Individual items are declared with the tag <LI>. For example: <OL> <LI> Item one <LI> Item two <LI> Item three </OL> Which is displayed by an HTML viewer as: 1. Item one 2. Item two 3. Item three The numbering system may be amended with the optional TYPE= command. The valid types are A,a,I,i,1 giving the following displays: A. Item one B. Item two C. Item three a. Item one b. Item two c. Item three I. Item one II. Item two III. Item three i. Item one ii. Item two iii. Item three 1. Item one 2. Item two 3. Item three The starting number may be defined by adding a START= command to the ordered list declaration, for example: <OL START=100> Which then produces the following display: 100. Item one 101. Item two 102. Item three The numbering order may be further amended during the list by adding a VALUE= command to a list item declaration, for example: <OL START=100> <LI> Item one <LI VALUE=500> Item two <LI> Item three </OL> Which produces the following display: 100. Item one 500. Item two 501. Item three An unordered list is displayed without numbering, but with bullets, for example: <UL> <LI> Item one <LI> Item two <LI> Item three </UL> Which is displayed by an HTML viewer as: _ Item one _ Item two _ Item three Some HTML viewers allow the bullet style to be redefined with a TYPE= command, accepting the values DISC, CIRCLE and SQUARE, for example: <UL TYPE=SQUARE> <LI> Item one <LI> Item two <LI> Item three </UL> Directory lists, specified by the <DIR> element, are similar to unordered lists. They represent a list of short items, typically up to 20 characters each. Items in a directory list may be arranged in columns, typically 24 characters wide, but may not be nested (unlike other lists). Some HTML viewers will further display directory lists in a different font to other lists. Menu lists are effectively the same as unordered lists, but link directory lists may not be nested and some HTML viewers can display them in a different font (notably Mosaic) to differentiate them from other unordered lists. Definition lists are used for listing terms and their definitions. A definition list is declared with the start-tag <DL>, and rather than using the list item tag <LI>, it uses a pair of tags, data-term and data-definition, <DT> and <DD> respectively. The data-definition is displayed indented from the preceding data-term. For example: <DL> <DT>Definition one <DD> Description of definition one which can wrap around to more than one line <DT>Definition two <DD> Description two which can wrap around<BR>to more than one line <DT>Definition three <DD> Description of definition three </DL> Which is displayed by an HTML viewer as: Definition one Description of definition one which can wrap around to more than one line Definition two Description of definition two which can also wrap around to more than one line Definition three Description of definition three Hyperlinks Hyperlinks enable the user of an HTML document to navigate through the currently loaded document (using local hyperlinks) and to external resources. All hyperlinks are defined in the HTML source code by anchors. An anchor is the following HTML code: <A HREF="destination">hyperlink display</A> For example: <A HREF="http://part_two.htm">Part Two</A> Would create a hyperlink to the resource "part_two.htm" which is expected by the HTML viewer to be an HTML document in the current directory (known as the base URI). The HTML viewer knows to terminate displaying text as a hyperlink by the anchor end-tag </A>. To the user, the hyperlink would be displayed as: Part Two An image could be used instead of the text, by replacing the hyperlink display text with an inline image command, for example: <A HREF="http://part_two.htm"><img src="part2.gif"></A> Local hyperlinks: Local hyperlinks, known as "Fragment Identifiers", are defined in a hypertext address by a # character following the resource. If navigation is required within the local document, the resource may be omitted so that a local hyperlink may look like: <A HREF="#introduction">Introduction</A> Selecting this hyperlink will cause the HTML viewer to search the current document for a declaration of "introduction". This declaration is achieved with the anchor name tag <A NAME=>, like this: <A NAME="Introduction"> Notice that the <A NAME=> tag does not have an end-tag, and is case insensitive. It doesn't matter if the anchor name is declared as "INTRODUCTION" or "Introduction" or even "introDuction" it will still be found by a hyperlink to "#introduction". Local hyperlinks can be added to hyperlinks to external documents to force the HTML viewer to load an external document and then navigate straight to a desired section within that document. For example: <A HREF="http://part_two.htm#section_3">Life and Love</A> Will create a hyperlink to the anchor "section_3" within the HTML document "part_two.htm". The following HTML document illustrates the use of local hyperlinks to form a table of contents to a document. Although this document is very short, you can see how the principle can be applied to longer and more complex documents. <HTML> <HEAD> </HEAD> <BODY> <TITLE>Local Hyperlink Example HTML document</TITLE> <P> <H2>Contents</H2> <OL> <LI><A HREF="#AEGIR">Aegir</A> <LI><A HREF="#AESIR">Aesir</A> <LI><A HREF="#ASGARD">Asgard</A> <LI><A HREF="#BALDER">Balder</A> <LI><A HREF="#BERSERKER">Berserker</A> <LI><A HREF="#BERTHA">Bertha</A> <LI><A HREF="#BRAGI">Bragi</A> </OL> <A NAME="AEGIR"><I><B>Aegir</B></I> <P> In Norse mythology, Aegir is the god of the sea. <P> <A NAME="AESIR"><I><B>Aesir</B></I> <P> The Aesir were the principal gods in Norse mythology. They lived in <A HREF="#ASGARD">Asgard</A>. <P> <A NAME="ASGARD"><I><B>Asgard</B></I> <P> In Norse mythology Asgard was the home of the gods. <P> <A NAME="BALDER"><I><B>Balder</B></I> <P> In Norse mythology, Balder was the son of Odin and Freya and husband of Nanna, and the best, wisest, and most loved of all the gods. He was killed, at Loki's instigation, by a twig of mistletoe shot by the blind god Hodur. <P> <A NAME="BERSERKER"><I><B>Berserker</B></I> <P> In Norse mythology, a Berserker was a warrior whose frenzy in battle transformed him into a wolf or bear howling and foaming at the mouth, and rendered him immune to sword and flame. <P> <A NAME="BERTHA"><I><B>Bertha</B></I> <P> In Norse mythology, Bertha is the goddess of spinning. <P> <A NAME="BRAGI"><I><B>Bragi</B></I> <P> In Norse mythology, Bragi is the god of poetry and eloquence. He was married to the goddess Iduna who dwelt in the underworld. </BODY> </HTML> Netscape introduced a number of new commands for hyperlinks. TARGET= can be used to open the hyperlink document in a new instance of the HTML viewer, or a specified frame. More about frames later. For example: <A HREF=next.htm TARGET=_BLANK>Next Document</A> When the hyperlink "Next Document" is selected, the document "next.htm" will be opened and displayed in a new instance of the HTML viewer. Hyperlinks are not restricted to other HTML documents. They can be used to access news servers, gopher servers, send mail and access ftp servers. A hyperlink to send mail uses the URL "mailto:" For example the following link attempts to send an email message to me: <A HREF="mailto:probertm@pins.co.uk">Feedback</A> Some HTML viewers will also support the addition of an optional subject, to save the user typing it in. For example: <A HREF="mailto:probertm@pins.co.uk" ?SUBJECT=Feedback>Feedback</A> Files can be sent to the user through FTP links, to send a specific file, use something like: < A HREF="ftp://server/path/filename">Download file</A> For example: Download <a href="ftp://ftp.pins.co.uk/seville/bbsc70.zip">BBSC70.ZIP</A> The HTML viewer will usually contact the FTP server, and attempt to connect using the name "anonymous" and sending the user's email address as a password. Linking to a gopher server is achieved with the URL gopher:// for example: <A HREF="gopher://gopher.pins.co.uk> Linking to a telnet service is achieved with the telnet:// URL, for example: <A HREF="telnet://pins.co.uk"> Linking to a WAIS index server is achieved with the wais:// URL, for example: <A HREF="wais://wais.pins.co.uk"> Linking to a news server is achieved with the nntp:// URL, for example: <A HREF="nntp://news.pins.co.uk"> Image Maps Image maps are a number of links defined as areas of a displayed image. They can be thought of as two distinct components, a map and an image. The map giving instructions as to the links and the image simply being a standard inline image. Each pixel of the image can be a link to another URL if required, but more usually different areas of the image link to different URLs. The following example illustrates the use of a simple image map. The image is displayed as normal with an <IMG> tag, but with the addition of the USEMAP command to indicate that the inline image is an image map. For example: <IMG SRC="map.gif" USEMAP="sample.htm"> The map component may be processed by the HTML viewer (a client side image map) or by the HTTP server if the HTML viewer cannot process maps. A server image map is defined by adding the command ISMAP to the <IMG> tag, for example: <IMG SRC="map.gif" USEMAP="sample.htm" ISMAP> In this case, the HTML viewer will expect the map information to be processed by the server. A client side image map (CSIM), however, is a map processed by the HTML viewer, which gets the map information from an HTML document found by the hyperlink following the USEMAP= command, in this case it follows later in the same document, and occurs between the <MAP> and </MAP> tags: <IMG SRC="map.gif" width=300 height=200 USEMAP="#sample"> <MAP NAME="sample"> <AREA SHAPE=RECT COORDS="60,80,120,100" HREF=map1.htm> <AREA SHAPE=RECT COORDS="140,130,210,160" HREF=map2.htm> <AREA SHAPE=RECT COORDS="80,20,220,50" HREF=map3.htm> </MAP> The first line tells the HTML viewer that this is a map, and assigns it a unique name, in this case "sample". The next three lines define three link areas within the image. Each area is defined with one the forms: <AREA SHAPE=RECT COORDS="top,left,bottom,right" HREF=URL> or <AREA SHAPE=CIRCLE COORDS="x,,y,radius" HREF=URL> or <AREA SHAPE=POLY COORDS="x,y,x2,y2,x3,y3....xn,yn" HREF=URL> These co-ordinates are pixel co-ordinates within the image and define a region within which the link occurs. The SHAPE=RECT command expects a rectangular region described by two pairs of co-ordinates. The SHAPE=CIRCLE command expects a circular region described by the co- ordinates of the circle centre, followed by the radius. The final example, SHAPE=POLY describes a multi-sided area. Here is the complete HTML example with blank lines inserted to make it easier to read and determine the individual areas: <HTML> <HEAD> <TITLE>Example Image Map</TITLE> </HEAD> <BODY> <H1 align=center>This Is An Image Map Example</H1> <CENTER> <IMG SRC="map.gif" width=300 height=200 USEMAP="#sample" ISMAP> </CENTER> <MAP NAME="sample"> <AREA SHAPE=RECT COORDS="60,80,120,100" HREF=map1.htm> <AREA SHAPE=RECT COORDS="140,130,210,160" HREF=map2.htm> <AREA SHAPE=RECT COORDS="80,20,220,50" HREF=map3.htm> </MAP> </BODY> </HTML> A NOHREF command, rather than an HREF= command, indicates that clicks in the defined area should not lperform a hyperlink. An HREF tag specifies where a click in that area should lead. Note that a relative anchor specification will be expanded using the URL of the map description as a base, rather than using the URL of the document from which the map description is referenced (important if the map definition is in a file separate to the main document). If a BASE tag is present in the document containing the map description, that URL will be used as the base. Any number of AREA tags may be specified within a map. If two areas intersect, the one which appears first in the map definition takes precedence in the overlapping region, and it's hyperlink jump will take place rather than the one specified in the later defined area. In this way, a default hyperlink may be made by defining an area covering the entire image, and placing this definition at the end of the map, so that any overlapping areas will take precedence over the default area. Advanced Formatting Multiple Spaces: HTML viewers reduce all white space into a single space character. If you want to add spaces between words, or padd a table column with white space you can use the &nbsp entity. For example: Hello &nbsp&nbsp&nbsp World Will display as Hello World Tables: The HTML table tags enable an HTML author to display information in a tabular format. A table is a grid of cells, each cell may contain a mixture of text and images and be a different size to the other cells in the table. A table is declared within the start-tag <TABLE> and end-tag </TABLE>. You can specify a border and its width in pixels for the table by adding a BORDER= command to the table start-tag, for example: <TABLE BORDER=1> Will give the displayed table a border 1 pixel wide. A wider border can be forced with BORDER=10 for example: <TABLE BORDER=10> The spacing between the cells can also be determined in pixels with the CELLSPACING= command. If you want a 10 pixel gutter between the table cells add the command CELLSPACING=10 to the table start-tag: <TABLE CELLSPACING=10> The spacing between the cell walls and the enclosed data can also be determined in pixels with the CELLPADDING= command. If you want a 10 pixel gutter between the table cell walls and the data in the cell add the command CELLPADDING=10 to the table start-tag: <TABLE CELLPADDING=10> Finally the width of the table can be expressed in pixels, or as a ratio of the document window width with the WIDTH= command; <TABLE WIDTH=50%> Putting this together we might want a table 200 pixels wide, with a cell spacing of 5 pixels and a border of 4 pixels width. The following table start-tag will achieve this: <TABLE CELLSPACING=5 WIDTH=200 BORDER=4> A caption can be included for the table with the caption tags <CAPTION> and </CAPTION>. The text or image contained within the caption tags will usually be displayed centred at the top of the table, just above the top border line. You can force the caption to be displayed below the table by adding the ALIGN=BOTTOM command to the caption start-tag, for example: <TABLE> <CAPTION>This caption displays above the table</CAPTION> </TABLE> <TABLE> <CAPTION ALIGN=BOTTOM>This caption displays below the table</CAPTION> </TABLE> Table cells are defined in terms or rows and within the rows, columns (either "table header" or "table data" cells). A table row is defined within the tags <TR> and </TR>, for example: <TABLE> <TR> ..... </TR> </TABLE> A table header column is defined within a row by the tags <TH> and </TH>, for example; <TABLE> <TR> <TH> This is a table! </TH> </TR> </TABLE> Table header cells are, by default, displayed in BOLD and aligned in the centre both horizontally and vertically. A table data column is defined within a row by the tags <TD> and </TD>, for example; <TABLE> <TR> <TD> This is a table! </TD> </TR> </TABLE> Table data cells are, by default, aligned left and vertically centred within the cell. Each table column may have individual alignment characteristics defined by the ALIGN= and VALIGN= commands which override the default settings. The ALIGN= command can be used to force the display to the left or right of the cell, and the VALIGN= command to force the display to the top or bottom of the cell for example: <HTML> <HEAD> <TITLE>Table Example</TITLE> </HEAD> <TABLE CELLSPACING=10 BORDER=1 WIDTH=100%> <CAPTION ALIGN=BOTTOM>Table Caption</CAPTION> <TR> <TD> Cell One is aligned to the left and in the centre vertically </TD> <TD> Cell Two <P>has multiple lines <P>in it <P>and is displayed to the left of the cell </TD> </TR> <TR> <TD ALIGN=CENTER VALIGN=TOP> Cell Three is centred horizontally, <P>at the top of the cell </TD> <TD ALIGN=RIGHT> Cell Four is another <P>multiple line cell <P>displayed to the right </TD> </TR> </TABLE> </BODY> </HTML> You can stop the HTML viewer from word-wrapping the text within a cell by adding the command NOWRAP to the cell definition, for example: <TD NOWRAP>This text will be displayed as one long line</TD> The size of the cell can be determined, to a degree, with the COLSPAN= and ROWSPAN= commands. These tell the HTML viewer how many columns and rows the cell is to span in relation to the rest of the table. For example: <HTML> <HEAD> <!-- Example of a simple table --> <TITLE>Simple Table</TITLE> </HEAD> <BODY> <TABLE BORDER=1> <TR><TH colspan=3>Protoplasm</TH></TR> <TR><TH>Plants</TH><TH>Invertebrates</TH><TH>Vertebrates</TH></TR> </TABLE> </BODY> </HTML> Blank or empty cells can be defined to force cells within a row to the right, for example: <TD></TD> Putting these concepts together, quite complex tables can be constructed, for example: Click here to view this table <HTML> <HEAD> <!-- Example of a complex table --> <TITLE>Evolution</TITLE> </HEAD> <BODY> <TABLE BORDER=1> <CAPTION>A Simplified Overview of Evolution</CAPTION> <TR><TH colspan=28>Protoplasm</TH></TR> <TR><TH colspan=27>Single-cell Plant Animals</TH><TD>Bacteria</TD></TR> <TR><TH colspan=5>Invertebrates</TH><TH colspan=3>Fungi</TH> <TH colspan=18>Vertebrates</TH><TD>Sponges</TD></TR> <TR><TH colspan=4>Ringed Worms</TH><TD>Jelly fish</TD> <TH colspan=3>Mosses</TH><TH colspan=16>Sharks</TH> <TD>Sea Squirts</TD><TD>Lancelets</TD></TR> <TR><TD>Cone shells</TD><TD>Spiders</TD><TD>Snails</TD><TD>Insects</TD> <TD></TD><TD>Conifers</TD><TD>Ferns</TD><TD>Flowering Plants</TD> <TH colspan=15>Amphibians</TH><TD>Bony Fishes</TD></TR> <TR><TD></TD><TD></TD><TD></TD><TD></TD><TD></TD><TD></TD><TD> </TD><TD></TD><TH colspan=13>Reptiles</TH><TD>Newts</TD><TD>Frogs</TD> </TR><TR><TD></TD><TD></TD><TD></TD><TD></TD><TD></TD><TD></TD> <TD></TD><TD></TD><TH colspan=11>Mammals</TH><TD>Crocodiles</TD> <TD>Lizards</TD></TR> <TR><TD></TD><TD></TD><TD></TD><TD></TD><TD></TD><TD></TD><TD> </TD><TD></TD><TD></TD><TH colspan=2>Ungulates</TH> <TH colspan=3>Carnivores</TH><TH colspan=3>Apes</TH><TD>Rodents</TD> <TD>Marsupials</TD></TR><TR><TD></TD><TD></TD><TD></TD><TD></TD> <TD></TD><TD></TD><TD></TD><TD></TD><TD></TD><TD>Cattle</TD> <TD>Deer</TD><TD>Cats</TD><TD>Civets</TD><TD>Weasels</TD> <TD>Monkeys</TD><TD>Gorillas</TD><TD>Man</TD></TR> </TABLE> </BODY> </HTML> Microsoft's Internet Explorer supports use of the BGCOLOR= command in the <TABLE> tag. It allows the background colour of the table to be specified using a standard rrggbb hex triplet. For example: <TABLE BGCOLOR="FFFFFF"> Microsoft's Internet Explorer includes support for the BORDERCOLOR= command which sets the border colour of the table. It takes as a parameter a rrggbb hex triplet. It is necessary for the BORDER attribute to be present in the main <TABLE> tag for border colouring to work. Microsoft's Internet Explorer allows use of the BORDERCOLORLIGHT= command to set independently, the lighter colour to be displayed on a 3-dimensional <TABLE> border. It is the opposite of BORDERCOLORDARK. It takes a colour parameter defined by a rrggbb hex triplet. It is necessary for the BORDER attribute to be present in the main <TABLE> tag for border colouring to work. Microsoft's Internet Explorer allows use of the BORDERCOLORDARK= command to set independently, the darker colour to be displayed on a 3- dimensional <TABLE> border. It is the opposite of BORDERCOLORLIGHT. It takes as a parameter a colour defined by a rrggbb hex triplet. It is necessary for the BORDER attribute to be present in the main <TABLE> element for border colouring to work. NOTE : The BGCOLOR, BORDERCOLOR, BORDERCOLORLIGHT and BORDERCOLORDARK attributes can also be used in <TH>, <TR> and <TD>tags, with the colour defined in the last element over-riding those defined before. E.g. if a <TD> element contains a BORDERCOLOR attribute setting, the setting specified will be used instead of any colour settings that may have been specified in the <TR> element, which in turn over-rides any colour settings in the <TABLE> element. Some HTML viewers support the placing of background images images inside the <TABLE>, <TH> and <TD> tags. If used in the <TABLE> element, the image will be tiled behind all of the table cells. For example: <TABLE BACKGROUND="myimage.gif"> Fixing Column Widths: The HTML viewer property of displaying images within table cells can be exploited to create fixed column widths in a table, where the data contained within the colmns varies in width. Normally, the HTML viewer generates columns based upon the widest element in the table column, creating uneven column widths. However, by forcing one cell in each column to a desired width, as wide or wider than the widest cell, you can create even column widths. One way to do this is to create a GIF image, of a single colour 2 x 2 pixels in size and make it transparent. Being so small this image will occupy a neglible amount of disk space and load even remotely very fast. Then this image can be used as an invisible element within a table cell to widen the cell as desired. The following example does not work with Mosaic, which does not support the image HEIGHT= and WIDTH= commands within a table cell, but it does work with Internet Explorer: <HTML> <HEAD> <!-- Example of a fixed width table --> <TITLE>Table</TITLE> </HEAD> <BODY> <TABLE BORDER=1> <CAPTION><H1>Fixed Width Table Demonstration</H1></CAPTION> <TR> <TD><IMG SRC=spacer.gif height=1 width=300><BR>1.00</TD><TD><IMG SRC=spacer.gif height=1 width=300><BR>8654.88</TD><TD><IMG SRC=spacer.gif height=1 width=300><BR>7430456.78</TD> <TR> <TD>46.00</TD><TD>87134.93</TD><TD>4031565.42</TD> <TR> <TD>51.00</TD><TD>554.10</TD><TD>440436.67</TD> <TR> <TD>11.00</TD><TD>6414.43</TD><TD>472816.72</TD> <TR> <TD>83.00</TD><TD>9824.01</TD><TD>734436.63</TD> </TR> </TABLE> </BODY> </HTML> Setting Table Borders: Internet Explorer supports the use of the FRAME= command which requires the BORDER= command to be set and affects the display of the table borders. It can accept any of the following parameters: void this removes all the external borders above this displays external borders at the top of the table only below this displays external borders at the bottom of the table only hsides this displays external borders at the horizontal sides of the table. I.e. at the top and bottom of the table. lhs this displays external borders at the left hand edges of the table only rhs this displays external borders at the right hand edges of the table only. vsides this displays external borders at both left and right hand edges of the table box this displays a box around the table (i.e. top, bottom, left and right hand sides) Internet Explorer supports the RULES= command. It requires the BORDER value to be set and may only be used in tables where the <THEAD>, <TBODY> and <TFOOT> tags have been declared. It affects the display of the internal table borders ("rules"). It can accept the following parameters: none this removes all the internal rules basic this displays horizontal borders between the <THEAD>, <TBODY> and <TFOOT> sections rows this displays horizontal borders between all rows cols this displays horizontal borders between all columns all this displays all the internal rules. Internet Explorer provides the <COLGROUP> and </COLGROUP> tag pair which can be used within a <TABLE> definition to group columns together to set their alignment properties. It accepts the following attributes: ALIGN="center|justify|left|right" This sets the text alignment within the column group. The default value is "center" VALIGN="baseline|bottom|middle|top" This sets the vertical text alignment within the column group. SPAN= This can be used to set the number of columns upon which the ALIGN and VALIGN attributes are to act. An example of an Internet Explorer enhanced table: <HTML> <HEAD> <!-- Example of an Internet Explorer Enhanced table --> <TITLE>IE Table</TITLE> </HEAD> <BODY> <TABLE BORDER FRAME=hsides RULES=cols> <COL ALIGN=left> <COLGROUP SPAN=3 ALIGN=center VALIGN=middle> <THEAD> <CAPTION ALIGN=center>This is the table caption</CAPTION> <TR> <TD>These</TD><TD>are</TD><TD>heading</TD><TD>cells</TD> </TR> </THEAD> <TBODY> <TR> <TD>These</TD><TD>are</TD><TD>body</TD><TD>cells</TD> </TR> <TR> <TD>X</TD><TD>X</TD><TD>X</TD><TD>X</TD> </TR> <TR> <TD>X</TD><TD>X</TD><TD>X</TD><TD>X</TD> </TR> <TR> <TD>X</TD><TD>X</TD><TD>X</TD><TD></TD> </TR> <TR> <TD>X</TD><TD>X</TD><TD>X</TD><TD></TD> </TR> <TR> <TD>X</TD><TD>X</TD><TD>X</TD><TD></TD> </TR> </TBODY> <TFOOT></TFOOT> </TABLE> </BODY> </HTML> CONTROLLING DOCUMENT BACKGROUNDS THE BACKGROUND ATTRIBUTE Recent versions of the proposed HTML 3.0 spec. have added a BACKGROUND attribute to the BODY tag. The purpose of this attribute is to specify a URL pointing to an image that is to be used as a background for the document. In Mosaic 2.1.1, Netscape and Internet Explorer, this background image is used to tile the full background of the document- viewing area. Thus specifying: <BODY BACKGROUND="aluminum.gif"> Document here </BODY> would cause whatever text, images, etc. appeared in that document to be placed on a tiled background image. If you prefer, a single large image may be displayed which does not scroll when the document window does by adding the command BGPROPERTIES=FIXED, for example: <BODY BACKGROUND="aluminum.gif" BGPROPERTIES=FIXED> Document here </BODY> THE BGCOLOR ATTRIBUTE Although not standard HTML, it is possible to define the colour of the background displayed by most modern HTML viewers, including Mosaic 2.1.1, Netscape Navigator and Microsoft Internet Explorer with the BGCOLOR= command. <BODY BGCOLOR="#rrggbb"> Document here </BODY> Where "#rrggbb" is a hexadecimal red-green-blue triplet used to specify the background colour. TEXT ATTRIBUTES Like the BGCOLOR= command, the TEXT= command controls the attribute of normal text displayed in a document. <BODY TEXT="#rrggbb"> Document here </BODY> THE LINK, VLINK, AND ALINK ATTRIBUTE These attributes let you control the colouring of link text. VLINK stands for visited link, and ALINK stands for active link. The default colouring of these is: LINK=blue, VLINK=purple, and ALINK=red. Again the format for these attributes is the same as that for the BGCOLOR= and TEXT= commands. For example: <BODY LINK="#rrggbb" VLINK="#rrggbb" ALINK="#rrggbb"> Document here </BODY> Putting it all together, here is an example from Netscape which illustrates a use of global colour attributes: <HTML> <HEAD> <TITLE>Colour Control Example</TITLE> </HEAD> <BODY BGCOLOR="#000000" TEXT="#F0F0F0" LINK="#FFFF00" VLINK="#22AA22" ALINK="#0077FF"> This is an example document. Text is light-grey on black, and <a href="nowhere.htm">anchors</a> are yellow at first, flashing blue-green when activated, and pale green if already visited. </BODY> </HTML> Notice that Mosaic and Internet explorer do not support the ALINK= command, it doesn't do any harm, unrecognised commands are simply ignored! This is just one of the many discrepancies between the various HTML viewers. Controlling individual text attributes: Some new HTML viewers, notably Netscape Navigator and Microsoft Internet Explorer support a new tag, <FONT>. The <FONT> tag enables the HTML author to specify a font size , colour and typeface. The size ranges from 1 to 7, smallest to largest. The colour takes a standard rgb hexadecimal triplet to define the attribute of the text within the <FONT> and </FONT> tags. For example: <FONT SIZE=6 COLOR="FF0000" FACE="Arial">This is a Large Red Heading in Arial Font</FONT> The font size can also be determined relative to the base font size using + and - in the FONT SIZE= command, for example: <FONT SIZE=+1>This is the next size up from the standard text</FONT> <FONT SIZE=-1>This is the next size down from the standard text</FONT> The base font size, colour and typeface can similarly be set with the BASEFONT command, for example: <BASEFONT SIZE=4 FACE="ARIAL" COLOR="FF0000"> Will set the base font size to slightly larger than the default, which is size 3. You can specify the name of different faces, for example: <font face="arial, courier, geneva"> the HTML viewer will use "courier" if "arial" is not available on the system, or "geneva" if courier is not available either. Preventing line breaks: Both Netscape and Internet Explorer support the <NOBR> and </NOBR> tag pair which prevent a long line from being broken. Instead the document view window must be scrolled to the right by the user with the scroll- bar to view the remainder of the text line. For example: <NOBR>The Abecedarian were the followers of Nicholas Storck, a 16th century German Anabaptist. They were so called because they rejected all worldly knowledge including learning the alphabet.</NOBR> Multi-Column Text: Currently, multi-column text only seems to be supported by Netscape Navigator. It is defined with the tag pair <MULTICOL COLS=n> and </MULTICOL>, for example: <MULTICOL COLS=4> This is multiple column text displayed by Netscape Navigator </MULTICOL> Displays the text within the multicol tags in 4 columns. The column widths and gutter between the columns can be defined by adding the WIDTH= and GUTTER= commands to the <MULTICOL> tag. Scrolling: Microsoft's Internet Explorer supports scrolling lines of text, which are declared by the <MARQUEE> tag. Only one line may be declared within each <MARQUEE> tag, line breaks <BR> being ignored. For example: <MARQUEE> This is a horizontal, animated, scrolling line of text! </MARQUEE> The <MARQUEE> tag also supports colour definition triplets for the background colour of the scrolling text, for example: <MARQUEE BGCOLOR="#FFFFFF"> This is a horizontal, animated, scrolling line of text! </MARQUEE> The behaviour of the scrolling text can be amended with the BEHAVIOUR= command. This supports three parameters; SCROLL, SLIDE and ALTERNATE. The default command is BEHAVIOUR=SCROLL, which displays the text scrolling across the screen. Adding the command BEHAVIOUR=ALTERNATE to the <MARQUEE> tag causes the scrolling text to scroll to the right edge of the document window, and then change direction, so that it scrolls left-to-right and then right- to-left. <MARQUEE BEHAVIOR=ALTERNATE> The SLIDE parameter causes the text to scroll on at the right-hand side of the document window and slide over to the left before stopping, with the text displayed at the left margin of the document window. The direction of the travelling text can be changed from right-to-left by the inclusion of the DIRECTION= command to the <MARQUEE> tag. For example, this will scroll from left-to-right, instead of the default right-to-left. <MARQUEE DIRECTION=RIGHT> Margins: Microsoft's Internet Explorer supports the definition of a left and a top margin with the commands LEFTMARGIN= and TOPMARGIN= which are added to the <BODY> tag, for example: <BODY LEFTMARGIN=10 TOPMARGIN=10> The margin size is measured in pixels and applies to the entire document. Buttons: Form buttons can be used as unusual, 3d links. For example, the following code creates a 3d button with the inscription "Link", which when pressed jumps to the URL www.pins.co.uk/upages/probertm/index.htm. <FORM action="http://www.pins.co.uk/upages/probertm/index.htm" METHOD=POST> <INPUT TYPE="submit" VALUE="Link"> </FORM> Inline Video: Microsoft's Internet Explorer allows the author to embed .AVI (Audio Video Interleave) video clips in HTML documents. This is done with the DYNSRC= command for the <IMG> tag. Using the <IMG> tag for this purpose makes it possible to add video clips to pages, but also have other browsers display still images in their place. For example; <IMG DYNSRC="video.avi" SRC="TheEarth.gif" WIDTH=50 HEIGHT=50 LOOP=INFINITE ALIGN=RIGHT> The DYNSRC= command specifies the address of a video clip to be displayed in the window. In the above example, Internet Explorer will play the movie file "video.avi"; while other browsers will display the picture "TheEarth.gif" You can add a START= command to the tag to specify when the video file should start playing. This attribute can be set to either FILEOPEN or MOUSEOVER. The default setting is FILEOPEN which means that the video will start playing as soon as the HTML document has finished loading. The MOUSEOVER parameter defines that the video will start playing when the user moves the mouse cursor over the animation. Both can be specified together if necessary. The CONTROLS command is a flag, which if specified causes a set of controls to be displayed under the video clip window. The LOOP= command specifies how many times a video clip will loop when activated. If n=-1, or if LOOP=INFINITE is specified, the video will loop indefinitely. The LOOPDELAY= command specifies, in milliseconds, how long a video clip will wait between play back loops. Embedded Objects: The <EMBED> tag allows you to put objects (video clips, sound or whatever) directly into an HTML page. The syntax is: <EMBED SRC="object_to_embed"> The <EMBED> element allows an HTML author to embed documents of any type. The HTML viewer needs to have an application which can view the data installed correctly on their machine, or have a "plug-in" (for Netscape Navigator) that can manipulate the embedded file format. The <EMBED> element can be used more or less the same as the <IMG> element and so accepts typical image embedding commands such as WIDTH, HEIGHT, BORDER, HSPACE, VSPACE. For example, to embed a sound file: <embed src="sound.wav"> Which are then downloaded to the HTML viewer, and played by a fitted soundcard, if the user has one and the HTML viewer supports sound. Frames Frames divide Web pages into multiple, scrollable regions which enable the HTML author to present information in a more flexible and useful fashion. Each region, or frame, has several features: 1. It can be given an individual URL, so it can load information independent of the other frames on the page; 2. It can be given a NAME, allowing it to be targeted by other URLs, and; 3. It can resize dynamically if the user changes the window's size. (Resizing can also be disabled, ensuring a constant frame size.) A frame is declared with the start-tag <FRAMESET> and the end-tag </FRAMESET> which replace the traditional <BODY> and </BODY> tags in a standard HTML document. The FRAMESET start-tag defines how many frames (regions) the viewer window will be divided into, and the sizes of these regions. The region sizes are defined in terms of pixel rows and columns. For example, to divide the document window into two equal frames, one above the other you can use the command; <FRAMESET ROWS=*,*> The ROWS= command takes a comma separated list of pixel heights in numbers, or in percentages or * to declare the pixel row height of each frame. Replacing a number with an asterisk * tells the HTML viewer to divide the available display area equally. The COLS= command is similar, but applies to the horizontal width of each frame. This example will split the display into two equal windows, and display a different URL in each, 1.htm in one and 2.htm in the other: <html> <head> <title>Frame Example</title> </head> <frameset rows=*,*> <frame src=1.htm> <frame src=2.htm> </frameset> </html> This example does the same, but displays divides the display vertically instead of horizontally; <html> <head> <title>Frame Example</title> </head> <frameset cols=*,*> <frame src=1.htm> <frame src=2.htm> </frameset> </html> Frames may be assigned names, by adding the NAME= command to the <FRAME> tag, for example: <FRAME SRC=1.HTM NAME=ONE> By default, the HTML viewer will decide whether or not to add scroll bars to the frame. If you want to suppress this, add the command SCROLLING=NO to the <FRAME> tag, for example: <FRAME SRC=1.HTM SCROLLING=NO> A top and a left margin may be applied to each frame with the MARGINHEIGHT= and MARGINWIDTH= commands within the <FRAME> tag. The margin will force a blank area to the left and top of the resource displayed within the frame. For example: <FRAME SRC=1.HTM MARGINHEIGHT=10 MARGINWIDTH=10> Hyperlinks within a frame, will by default load new resources into the current frame. However, this can be amended so that the new document is loaded into a different frame. If you have named your frames with the NAME= command, then the target frame can be easily defined with: <A HREF=new_doc.htm TARGET=named_frame>Link</A> Where "named_frame" is the name of the frame you want "new_doc.htm" to be loaded into. There are three predefined frame names: _top, _self and _parent. _self refers to the current frame, and is the default target for loading hyperlinked documents. _parent refers to the frame which spawned the current frame, and _top refers to the entire display window. Here is a complete example comprised of a number of separate source files. The name of each source file is in the title in brackets, e.g. (test.htm): <html> <head> <title>Frame Test (test.htm)</title> </head> <frameset rows=*,*> <frame src=test1.htm name=test1> <frame src=test2.htm name=test2> </frameset> </html> <html> <head> <title>Frame Test (test1.htm)</title> </head> <body> This is file TEST1.HTM </body> </html> <html> <head> <title>Frame Test (test2.htm)</title> </head> <frameset cols=*,*> <frame src=test_a.htm name=testa> <frame src=test_b.htm name=testb> </frameset> </html> <html> <head> <title>Frame Test (test_a.htm)</title> </head> <body> This is file TEST_A.HTM </body> </html> <html> <head> <title>Frame Test (test_b.htm)</title> </head> <body> This is file TEST_B.HTM <P> <A href=test_c.htm target = test1>Load test_c.htm</A> </body> </html> <html> <head> <title>Frame Test (test_c.htm)</title> </head> <body> This is file TEST_C.HTM </body> </html> Frames are a fairly recent innovation to the HTML language, and not very many HTML viewers handle them. For those which don't there is the tag pair <NOFRAMES> and </NOFRAMES> which declare a section of the document to be displayed if the HTML viewer does not recognise frames. This can be used to display a message or alternative form of the document when viewed by HTML viewers which do not recognise frames, for example: <html> <head> <title>Frame Test</title> </head> <noframes> This will only be displayed if the HTML viewer does not support frames </noframes> <frameset rows=*,*> <frame src=test1.htm name=test1> <frame src=test2.htm name=test2> </frameset> </html> Floating Frames: Microsoft's Internet Explorer has introduced the floating frame, specified with the tag pair <IFRAME> and </IFRAME>. These behave in a manner a cross between an inline image and a frame. That is, documents can be loaded into a floating frame just like any other frame, but floating frames are displayed as though they were an inline image. For example: <IFRAME NAME="frame1" width="400" height="200" SRC="welcome.htm"></IFRAME> Any text specified between the tags will be displayed to HTML viewers which do not support floating frames, instead of the frame. For example: <IFRAME NAME="frame1" width="400" height="200" SRC="welcome.htm"> Sorry! This site can only be viewed with Internet Explorer </IFRAME> Forms A form is a template for a form data set and an associated method and action URI used on the WWW. Forms have no relevance to local HTML publishing. A form data set is a sequence of name/value pair fields. The names are specified on the NAME attributes of form input elements, and the values are given initial values by various forms of markup and edited by the user. The resulting form data set is used to access an information service as a function of the action and method. Forms elements can be mixed in with document structuring elements. For example, a PRE element may contain a FORM element, or a FORM element may contain lists which contain INPUT elements. This gives considerable flexibility in designing the layout of forms. Form Elements <FORM> The <FORM> element contains a sequence of input elements, along with document structuring elements. The attributes are: ACTION= specifies the action URI for the form. The action URI of a form defaults to the base URI of the document. METHOD= selects a method of accessing the action URI. The set of applicable methods is a function of the scheme of the action URI of the form. See section Query Forms: METHOD=GET and section Forms with Side-Effects: METHOD=POST. ENCTYPE = specifies the media type used to encode the name/value pairs for transport, in case the protocol does not itself impose a format. <INPUT> The <INPUT> element represents a field for user input. The TYPE= attribute discriminates between several variations of fields. The <INPUT> element has a number of attributes. The set of applicable attributes depends on the value of the TYPE= attribute. The default vaule of the TYPE attribute is `TEXT', indicating a single line text entry field. (Use the TEXTAREA element for multi-line text fields.) Required attributes are: NAME, the name for the form field corresponding to this element. The optional attributes are MAXLENGTH which constrains the number of characters that can be entered into a text input field. If the value of MAXLENGTH is greater the the value of the SIZE attribute, the field should scroll appropriately. The default number of characters is unlimited. SIZE specifies the amount of display space allocated to this input field according to its type. The default depends on the user agent. VALUE defines the initial value of the field. For example: <p> Street Address: <input name=street><br> Town: <input name=city size=20 maxlength=20><br> Post Code: <input name=post size=10 maxlength=10><br> An INPUT element with `TYPE=PASSWORD' is a text field as above, except that the value is obscured as it is entered. For example: <p>Name: <input name=login> Password: <input type=password name=passwd> An INPUT element with `TYPE=CHECKBOX' represents a boolean choice. A set of such elements with the same name represents an n-of-many choice field. Required attributes are: NAME a symbolic name for the form field corresponding to this element or group of elements. VALUE the portion of the value of the field contributed by this element. Optional attributes are: CHECKED indicates that the initial state is on. For example: <p> What flavours do you like? <input type=checkbox name=flavour value=vanilla> Vanilla<br> <input type=checkbox name=flavour value=strawberry> Strawberry<br> <input type=checkbox name=flavour value=chocolate checked> Chocolate<br> An INPUT element with `TYPE=RADIO' represents a boolean choice. A set of such elements with the same name represents a 1-of-many choice field. The NAME and VALUE attributes are required as for check boxes. Optional attributes are: CHECKED indicates that the initial state is on. At all times, exactly one of the radio buttons in a set is checked. If none of the INPUT elements of a set of radio buttons specifies `CHECKED', then the user agent must check the first radio button of the set initially. For example: <p> Which is your favourite? <input type=radio name=flavour value=vanilla> Vanilla<br> <input type=radio name=flavour value=strawberry> Strawberry<br> <input type=radio name=flavour value=chocolate> Chocolate<br> An INPUT element with `TYPE=IMAGE' specifies an image resource to display, and allows input of two form fields: the x and y coordinate of a pixel chosen from the image. The names of the fields are the name of the field with `.x' and `.y' appended. `TYPE=IMAGE' implies `TYPE=SUBMIT' processing; that is, when a pixel is chosen, the form as a whole is submitted. The NAME attribute is required as for other input fields. The SRC attribute is required and the ALIGN is optional as for the IMG element. For example: <p> Choose a point on the map: <input type=image name=point src="map.gif"> An INPUT element with `TYPE=HIDDEN' represents a hidden field.The user does not interact with this field; instead, the VALUE attribute specifies the value of the field. The NAME and VALUE attributes are required. For example: <input type=hidden name=context value="l2k3j4l2k3j4l2k3j4lk23"> An INPUT element with `TYPE=SUBMIT' represents an input option, typically a button, that instructs the user agent to submit the form. Optional attributes are: NAME indicates that this element contributes a form field whose value is given by the VALUE attribute. If the NAME attribute is not