HTML Quick Reference
The HyperText Markup Language (HTML) is composed of a set of elements
that define a document and guide its display. This document presents a
concise reference guide to HTML, listing the most commonly used elements
from Versions 1 and 2 of HTML, and giving a brief description of those
elements.
Users should be aware that HTML is an evolving language, and different
World-Wide Web browsers may recognize slightly different sets of HTML
elements. For general information about HTML including plans for new versions,
see http://www.w3.org/hypertext/WWW/MarkUp/MarkUp.html.
Introduction
An HTML element may include a name, some attributes and some text or
hypertext, and will appear in an HTML document as
<tag_name> text </tag_name>
<tag_name attribute_name=argument> text </tag_name>,
or just
<tag_name>
For example:
<title> My Useful Document </title>
and
<a href="argument"> text </a>
An HTML document is composed of a single element:
<html> . . . </html>
that is, in turn, composed of head and body elements:
<head> . . . </head>
and
<body> . . . </body>
To allow older HTML documents to remain readable, <html>,
<head>, and <body> are actually optional
within HTML documents.
Elements usually placed in the head element
<isindex>
- Specifies that the current document describes a database that can
be searched using the index search method appropriate for whatever client
is being used to read the document. For example, a Lynx user will use
the "s" keyboard command.
<title> . . . </title>
- Specify a document title. Note that the title will not appear on the
document as is customary on printed documents. It will usually appear
in a window bar identifying the contents of the window. HTML header
tags perform the functions usually reserved for titles.
<base href="URL">
- Specify the name of the file relative to which partially qualified
pathnames in URLs should be interpreted. If not otherwise specified
the URL containing the document being displayed is used as the base.
<link rev="RELATIONSHIP" rel="RELATIONSHIP" href="URL">
- The link tag allows you to define relationships between the document
containing the link tag and the document specified in the "URL". The
rel attribute specifies the relationship between the HTML
file and the Uniform Resource Locator (URL). The rev attribute
(for "reverse") specifies the relationship between the URL and the HTML
file. For example, <link rev="made" href="URL"> indicates
that the file maker or owner is described in the document identified
by the URL. (Note that link tags are not displayed on the screen as
part of the document. They define static relationships, not hypertext
links.)
Elements usually placed in the body element
The following sections describe elements that can be used in the body of
the document.
Text Elements
<p>
- The end of a paragraph that will be formatted before it is displayed
on the screen.
<pre> . . . </pre>
- Identifies text that has already been formatted (preformatted) by
some other system and must be displayed as is. Preformatted text may
include embedded tags, but not all tag types are permitted. The
<pre>
tag can be used to include tables in documents.
<listing> . . . </listing>
- Example computer listing; embedded tags will be ignored, but embedded
tabs will work. This is an archaic tag.
<xmp> . . . </xmp>
- Similar to
<pre> except no embedded tags will be
recognized.
<plaintext>
- Similar to
<pre> except no embedded tags will be
recognized, and since there is no end tag, the remainder of the document
will be rendered as plain text. This is an archaic tag. Note that some
browsers actually recognize a </plaintext> tag, even
though it is not defined by the standard.
<blockquote> . . . </blockquote>
- Include a section of text quoted from some other source.
Hyperlinks or Anchors
<a name="anchor_name"> . . . </a>
- Define a target location in a document
<a href="#anchor_name"> . . . </a>
- Link to a location in the base document, which is the document containing
the anchor tag itself, unless a base tag has been specified.
<a href="URL"> . . . </a>
- Link to another file or resource
<a href="URL#anchor_name"> . . . </a>
- Link to a target location in another document
<a href="URL?search_word+search_word"> . . . </a>
- Send a search string to a server. Different servers may interpret
the search string differently. In the case of word-oriented search engines,
multiple search words might be specified by separating individual words
with a plus sign (+).
An anchor must include a name or href attribute,
and may include both. There are several optional attributes, but they are
rarely encountered.
The structure of a Uniform Resource Locator (URL) may be expressed as:
-
- resource_type:additional_information
where the possible resource types include: file, http,
news, gopher, telnet, ftp,
and wais, among others, and each resource type relates to a
specific server type. Since each server performs a unique function, each
resource type requires different additional_information. For
example http and gopher URLs will have a structure
like:
-
- resource_type://host.domain:port/pathname
The colon followed by an integer TCP port number is optional, and is used
when a server is listening on a non-standard port.
Strictly speaking, the anchor_name and search_word
information included in the name and href attributes
in the examples above are part of the URL. They are presented as separate
entities for simplicity. A more complete description of URLs is presented
in
http://www.w3.org/hypertext/WWW/Addressing/Addressing.html
Headers
<h1> . . . </h1> Most prominent
header
<h2> . . . </h2>
<h3> . . . </h3>
<h4> . . . </h4>
<h5> . . . </h5>
<h6> . . . </h6> Least prominent
header
Logical Styles
<em> . . . </em>
- Emphasis
<strong> . . . </strong>
- Stronger emphasis
<code> . . . </code>
- Display an HTML directive
<samp> . . . </samp>
- Include sample output
<kbd> . . . </kbd>
- Display a keyboard key
<var> . . . </var>
- Define a variable
<dfn> . . . </dfn>
- Display a definition (not widely supported)
<cite> . . . </cite>
- Display a citation
Physical Styles
<b> . . . </b>
- Boldface
<i> . . . </i>
- Italics
<u> . . . </u>
- Underline
<tt> . . . </tt>
- Typewriter font
Definition list/glossary: <dl>
<dl>
<dt> First term to be defined
<dd> Definition of first term
<dt> Next term to be defined
<dd> Next definition
</dl>
The <dl> attribute compact can be used to
generate a definition list requiring less space.
Present an unordered list: <ul>
<ul>
<li> First item in the list
<li> Next item in the list
</ul>
Present an ordered list: <ol>
<ol>
<li> First item in the list
<li> Next item in the list
</ol>
Present an interactive menu: <menu>
<menu>
<li> First item in the menu
<li> Next item
</menu>
Present a directory list of items: <dir>
<dir>
<li> First item in the list
<li> Second item in the list
<li> Next item in the list
</dir>
Items should be less than 20 characters long.
Entities
&keyword;
- Display a particular character identified by a special keyword. For
example the entity
& specifies the ampersand (
& ), and the entity < specifies the less than
( < ) character. Note that the semicolon following the keyword is
required, and the keyword must be one from the lists presented in:
- http://www.w3.org/pub/WWW/MarkUp/html-spec/html-spec_9.html#SEC9.7
&#ascii_equivalent;
- Use a character literally. Again note that the semicolon following
the ASCII numeric value is required.
HTML Forms Interface
The HTML forms interface allows document creators to define HTML documents
containing forms to be filled out by users. When a user fills out the form
and presses a button indicating the form should be "submitted," the information
on the form is sent to a server for processing. The server will usually
prepare an HTML document using the information supplied by the user and
return it to the client for display.
The following tags implement the forms interface:
<form> . . . </form>
<input>
<select> . . . </select>
<option>
<textarea> . . . </textarea>
The last four tags can only be used within a <form> .
. . </form> element.
Define a form
<form> . . . </form>
Defines a form within an HTML document. A document may contain multiple
<form> elements, but <form> elements
may not be nested. Note that non-form tags can be used within a <form>
element. Attributes and their arguments:
action="URL":
- The location of the program that will process the form.
method=data_exchange method
- The method chosen to exchange data between the client and the program
started to process the form: One of
get or post.
post is preferred for most applications.
- Example:
-
<form action="http://www.ku.edu/cgi-bin/register" method=post>
. . . </form>
Define an input field
<input> (there is no ending tag)
Defines an input field where the user may enter information on the form.
Each input field assigns a value to a variable which has a specified name
and a specified data type. Attributes and their arguments:
type="variable_type"
- Specifies the data type for the variable, where:
-
type="text" and type="password" fields
accept character data
-
type="checkbox" fields are either selected or not
-
type="radio" fields of the same name allow selection
of only one of the associated values
-
type="submit" defines an action button that sends
the completed form to the query server
type="reset" defines a button that resets the form
variables to their default values
type="hidden" defines an invisible input field whose
value will be sent along with the other form values when the form
is submitted. This is used to pass state information from one script
or form to another.
type="image"defines an image map within a form and
returns the coordinates of a mouse click within the image.
name="textstring"
- where
textstring is a symbolic name (not displayed) identifying
the input variable as in:
<input type="checkbox" name="box1">
value="textstring"
- where the meaning of
textstring depends on the argument
for type.
- For
type="text" or type="password",
textstring is the default value for the input
variable. Password values will not be shown on the user's form.
Anything entered by the user will replace any default value defined
with this attribute.
- If
type="checkbox" or type="radio",
textstring is the value that will be sent to the server
if the checkbox is "checked".
- For
type="reset" or type="submit", textstring
is a label that will appear on the submit or reset button in place
of the words "submit" and "reset".
checked
- No arguments. For
type="checkbox" or type="radio",
if checked is present the input field is "checked"
by default.
size="display_width"
- where
display_width is an integer value representing
the number of characters displayed for the type="text"
or type="password" input field.
maxlength="string_length"
- where
string_length is the maximum number of characters
allowed within type="text" or type="password"
variable values. This attribute is only valid for single line "text"
or "password" fields.
Define a select field
<select> . . . </select>
Defines and displays a set of optional list items from which the user
can select one or more items. This element requires an <option>
element for each item in the list. Attributes and their arguments:
name="textstring"
- where
textstring is the symbolic identifier for the select
field variable.
size="list_length"
- where
list_length is an integer value representing the
number of <option> items that will be displayed at
one time.
multiple
- No arguments. If present, the
multiple attribute allows
selection of more than one <option> value.
Define a select field option
<option>
Within the <select> element the <option>
tags are used to define the possible values for the select
field. If the attribute selected is present then the option
value is selected by default. In the following example all three options
may be chosen but bananas are selected by default.
<select multiple>
<option>Apples
<option selected>Bananas
<option>Cherries
</select>
Define a text area
<textarea> . . . default text . . . </textarea>
Defines a rectangular field where the user may enter text data. If "default
text" is present it will be displayed when the field appears. Otherwise
the field will be blank. Attributes and their values:
name="textstring"
textstring is a symbolic name that identifies the <textarea>
variable.
rows="num_rows" and cols="numcols"
- Both attributes take an integer value which represents the lines and
number of characters per line in the
<textarea> to
be displayed.
Miscellaneous
<!-- text -->
- Place a comment in the HTML source
<address> . . . </address>
- Present address information
<img src="URL" alt="Alternate Text">
- Embed a graphic image in the document. Attributes:
src
- Specifies the location of the image.
alt
- Allows a text string to be put in place of the image in clients
that cannot display images.
align
- Specify a relationship to surrounding text. The argument for
align
can be one of top, middle, or bottom.
ismap
- If
ismap is present and the image tag is within an
anchor, the image will become a "clickable image". The pixel coordinates
of the cursor will be appended to the URL specified in the anchor
if the user clicks within the ismap image. The resulting URL will
take the form "URL?m,n" where m and n are integer coordinates, and
the URL will specify the location of a program that will examine
the pixel coordinates, and return an appropriate document.
<br>
- Forces a line break immediately and retains the same style.
<hr>
- Places a horizontal rule or separator between sections of text.
Additional Information
For a tutorial introduction to HTML see:
http://www.ncsa.uiuc.edu/General/Internet/WWW/HTMLPrimer.html.
For an introduction to forms within HTML see:
An Instantaneous Introduction to CGI Scripts and HTML Forms.
For general information about HTML, see
http://www.w3.org/hypertext/WWW/MarkUp/MarkUp.html
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