(divisions)
Netscape Navigator 2.0 supports the left, right, and center
ALIGN attributes of both P and DIV.
Image maps are an important feature of the point-and-click in-
terface that makes the World Wide Web so popular. The most com-
mon use of image maps is to allow users to access different
documents by clicking on different areas in an image.
There are several limitations of the current image map imple-
mentation as it applies to this use. First, it only works over
the HTTP protocol, making it unusable for reading local files
or files accessed via alternate protocols. Second, a server
transaction is required merely to determine where the link is
directed. This can degrade performance noticeably when access-
ing distant sites. Third, unlike for normal links, there is no
way for a browser to provide visual feedback to the user by
showing where a portion of an image map leads before the user
actually clicks on it. Lastly, the implementation of image maps
is server-dependent, compromising portability of documents.
While HTML+1 contains provisions for "hypertext buttons" on im-
ages via use of the FIG element, this method is an unworkable
short-term solution for several reasons. First, complete sup-
port of the FIG element requires significant additional pro-
cessing by the browser. Second, it cannot degrade gracefully on
browsers that do not support it. Third, it requires the map de-
scription to be specified when the image appears, which is in-
appropriate for some applications. The extension to support
client-side image maps addresses these issues.
SYNTAX
Adding a USEMAP attribute to an IMG element indicates that it
is a client-side image map. The USEMAP attribute can be used
with the ISMAP attribute to indicate that the image can be pro-
cessed as either a client-side or server-side image map. The
argument to USEMAP specifies which map to use with the image,
in a format similar to the HREF attribute on anchors. If the
argument to USEMAP starts with a "#", it is assumed to be in
the same document as the IMG tag. A few examples would be:
You can only click here if your browser supports client-side image maps:
This image map will work regardless:
Clicking here will take you to a page with an error message if
you don't have client-side image map support:
The different regions of the image are described using a MAP
element. The map describes each region in the image and indi-
cates where it links. The basic format for the MAP element is
as follows:
The name specifies the name of the map so that it can be refer-
enced by an IMG element. The shape gives the shape of this
area. Currently supported shapes include rectangles (RECT),
polygons (POLY), circles (CIRCLE), and default (DEFAULT), but
the syntax is defined in a way that allows other shapes to be
added. If the SHAPE tag is omitted, SHAPE="RECT" is assumed.
The COORDS tag gives the coordinates of the shape, using image
pixels as the units. For a rectangle, the coordinates are given
as "left,top,right,bottom". The rectangular region defined in-
cludes the lower right corner specified (i.e. to specify the
entire area of a 100-by-100-pixel image, the coordinates would
be "0,0,99,99"). Circles are defined as a center point and then
a radius (a total of three numbers).
The NOHREF tag indicates that clicks in this region should per-
form no action. 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. If a BASE tag is present in the
document containing the map description, that URL will be used
as the base.
An arbitrary number of AREA tags may be specified. If two areas
intersect, the one that appears first in the map definition
takes precedence in the overlapping region. For example, a but-
ton bar in a document might use a 160-by-60-pixel image and ap-
pear like this:
This example includes a region encompassing the entire image
with a NOHREF tag, but this is actually redundant. Any region
of the image that is not defined by an AREA tag is assumed to
be NOHREF.
DISCUSSION
This syntax provides maximum flexibility to the document author
for dealing with browsers that do not support this extension,
since such browsers will ignore the MAP and AREA elements. If
the document resides on an HTTP server, the server can still
provide ISMAP-style support. Otherwise, the author can choose
to have the image not appear as an anchor at all, or can choose
to have a click anywhere within it lead to another page, per-
haps providing an equivalent textual list of options.
The demand for a non-HTTP-based mechanism for image maps will
also increase as archives of material in HTML format begins to
appear on CD-ROM. The expected increase in pay-per-access
servers will also lead to users saving copies of documents lo-
cally, which they would then expect to function identically to
those on the original server. The extensions described here
could serve as a basis to satisfy these needs.
REFERENCES
1. Ragget, Dave, HTML+ Discussion Document
(http://www.w3.org/hypertext/WWW/MarkUp/HTMLPlus/htmlplus_1.html)
Previously, form input was limited to input boxes and other
simple elements like checkboxes and radio buttons. Now you can
write forms that ask for files as input. A new ENCTYPE at-
tribute on the FORM tag allows you to write forms that take
files as input. An example of such a form would be:
Популярность: 20, Last-modified: Thu, 27 Jun 1996 11:00:45 GmT