HTML 4.0 Sourcebook
(Publisher: John Wiley & Sons, Inc.)
Author(s): Ian S. Graham
ISBN: 0471257249
Publication Date: 04/01/98

In this case, the referred handler (a Java program) is located on one remote server, while the data to be viewed is located on another.

Nested OBJECTS

OBJECT elements can be nested, allowing a cascade of possible object embeddings and handlers. An example of the associated OBJECT markup is (commentary in italics):

<OBJECT  ... (preferred data/handler) >
   <OBJECT ... (second choice ...) >
      <OBJECT ... (third choice ...) >
          HTML alternative to OBJECT ...
      </OBJECT>
   </OBJECT>
</OBJECT>

The browser would then work its way in through the OBJECTs, stopping when it finds one it can successfully process and ignoring any subsequent OBJECTs. Note that this is not properly supported by current browsers, so that for now you should avoid nesting OBJECTs.

Backwards Compatibility

To a large extent, OBJECT elements should be compatible with browsers that do not understand OBJECT. For example, OBJECT elements used to invoke imagemaps can contain, as an alternative, the regular IMG element markup, while more complex OBJECTs might contain EMBED elements with similar or equivalent functionality. This, however, hinges on proper support of OBJECT—unfortunately, current implementations are buggy and incomplete, such that this approach is not feasible.

The specification for OBJECT is presented below. This is followed by an overview of the changes to the PARAM and A elements introduced in support of OBJECT.

OBJECT Element: Embed an Arbitrary Data/Program Object

ALIGN=“absbottom,” “absmiddle,” “baseline,” “bottom,” “left,” “middle,” “right,” “texttop” (optional) Specifies the desired alignment of the object. The values are the same as those used for the IMG element, and you are refereed there (Chapter 6) for a description of the meanings.

ARCHIVE=“space–separated URLs” (optional; not currently supported)Contains a space–separated list of URLs that reference resources relevant to the object. Such URLs could reference resources specified by the CLASSID or DATA attributes. A browser may use these URLs to preload the declared archives, prior to actually using them. Thus, one OBJECT may be used to pre–load archives that are needed by subsequent OBJECTs. Relative URLs are allowed and are interpreted relative to the URL specified by the CODEBASE attribute.

BORDER=“length” (optional; not supported by Netscape Navigator 4)Specifies the thickness of the border to be drawn around the object, should it be within an active anchor element. The thickness can be specified in any of the supported length units—at present, the only supported units are pixels (the default), in which case the height is simply given as an integer. The value of “0” indicates that the object should be drawn without borders.

CLASSID= “url” (optional; one of DATA or CLASSID is required) Specifies the URL of the program code that will implement the object: The URL can either reference an Internet–accessible resource, or it can reference a class name using a class–type specific URL naming scheme. An example of the former is a URL that references a remote java class object, such as:

CLASSID=“<http://www.server.org/path/dir/myapplet.class>”

An example of the latter is the clsid URL scheme introduced by Microsoft for identifying Component Object Model (COM) objects. For example:

CLASSID=“clsid:D27CDB6E–AE6D–11CF–96B8–444553540000”

Clsid URLs are discussed in more detail in Chapter 8.

CODEBASE=“string” (optional) Specifies a URL that references program code required by the code specified by CLASSID, and which otherwise cannot be located by the CLASSID value. An example is a CLASSID that references an applet, with a CODEBASE that references the associated class/code library.

CODETYPE=“string” (optional; not supported by Netscape Navigator 4)Specifies the MIME type of the code referenced by the CLASSID attribute (CLASSID references the program object to be loaded). This is a hint to the browser—–a browser can use this information to avoid downloading objects it does not support.

DATA=“string” (optional; one of DATA or CLASSID is required)Specifies the URL of the data to be loaded. This can, for example, be an image file, a spreadsheet data set, or a VMRL world scene. TYPE can specify the MIME type of the data referenced by DATA. If CLASSID is absent, the browser will use the MIME type specified by TYPE or the type determined by downloading the actual data file to establish a program to handle the data type. In other words, the data type is used to determine an appropriate default value for CLASSID.

DECLARE (optional; not currently supported)Indicates that the object should be declared, but not instantiated. That is, the object is made available to the system, but is not started until invoked by some other resource. This allows objects to be loaded for future use.

HEIGHT=“length” (mandatory) Specifies the desired height of the box enclosing the object, in pixels. In principle, HEIGHT can be used to rescale the object to the specified height. Whether or not this is possible depends on the object being embedded.

HSPACE=“length” (optional) Specifies the desired horizontal spacing to leave to the left and right of the object, in pixels.

ID=“name” (optional) Specifies a name token identifier for the object. This identifier can be used by the browser, script programs, or other objects embedded in the document to identify and communicate with the ID–labeled object.

NAME=“string” (optional) Specifies a variable name, analogous to the NAME attribute of SELECT, INPUT, and TEXTAREA elements. This is only relevant if the OBJECT is inside a FORM. In this case, the presence of a NAME tells the browser that data from the object should be included with the form data when the form is submitted (it is the responsibility of the object author to ensure that the data are made available to the FORM, and in the correct format). If NAME is absent, then the object and the form are unrelated.

STANDBY=“string” (optional; not currently supported)Specifies a short text string (including character and entity references, but not HTML markup) that can be displayed to the user while the object is loading.