The ISINDEX element indicates that the browser must allow the user to search
an index by entering keywords. This legacy element from early HTML is much
less common now that complex form capability is possible. Although it can be
placed in other areas of an HTML document, it is usually found contained in the HEAD element.
This optional attribute specifies a method or protocol for accessing
the ACTION URL. A METHOD of GET will send the
ISINDEX value in a query URL that looks like: URL?value
where URL is the URL specified by the ACTION attribute, or
the current document URL if no ACTION attribute was specified.
In the POST method, the contents
are sent in environment variables in the HTTP transaction.
This is an SGML Document Access
(SDA) attribute. SDA attributes are designed to transform HTML (and
other SGML-based documents) to the ICADD
DTD - which is used in creating accessible documents for users with
visual disabilities (rendering in Braille, large print, speech
synthesis, etc.) The attribute value specifies content to be added
BEFORE the original element (in this case the string
"<Para>[Document is indexed/searchable.]</Para>") when the
SDA document is rendered.
"<Para>[Document is indexed/searchable.]</Para>"
Because this element is not widely used, the addition of new elements that
would be supported parents of ISINDEX may break some browsers. It is also
not widely used anywhere but in the HEAD section, which some
parsers may take for granted.
The beta versions of Internet Explorer 4.0 did not support this element
at all - the final version of IE 4.0, however, supported it again.
The default method for sending ISINDEX data is via the GET method (the
data is appended to a URL as an argument.)
In Netscape 1.0-4.x, when data is sent via POST, it is sent as a
name/value pair (exactly like it is done with normal forms.) The data
is sent as: The ISINDEX value is what is entered by the user, and the
variable name it is assigned to is "isindex." If the GET method is
used, the value is the only data that is sent.
Opera 4.x: Assigning event handlers to this element will only trigger
on the isindex surrounding area, NOT the ISINDEX text input field -
this seems like incorrect behavior to me.
Netscape 6 Beta Warning: Support for this element
was not added to Mozilla/Netscape 6 until Beta 3 - in Betas 1 and 2 this
element was not supported at all.