The OBJECT element supplies the browser with information to load and render data types that are not natively supported by the browser. If the browser must load some external program (a Java applet, a plugin, or some other helper), the information about the content that is to be rendered is contained by the OBJECT element, its attributes, and optionally, associated PARAM elements nested inside of it. Although today's browsers recognize elements such as APPLET and EMBED, the HTML specification indicates that the trend is to combine all of this into the OBJECT element.

The HTML 4.0 specification allows nesting of OBJECT elements to give the browser a chance to load alternate content if no plugin, or other necessary content aids, is available in the browser. Essentially, the browser should be able to walk through nested OBJECT elements until it finds one it can handle. For example, the outer OBJECT element may try to load an MPEG2 video; if no player is available, the browser looks for the next nested OBJECT, which is a JPEG still image from the video; if the browser is not a graphical browser, it would render some straight HTML that is the most nested item (although not as an OBJECT element) within the hierarchy of nested OBJECTs:

<DIV>
<OBJECT data="proddemo.mpeg" type="application/mpeg">
    <OBJECT data="prodStill.jpg" type="image/jpeg">
        The all-new Widget 3000!
    </OBJECT>
</OBJECT>
</DIV>

HTML 4.0 details a framework for turning OBJECT elements consisting of images into client-side image maps. The syntax is a little different from the MAP and AREA elements used for IMG element image maps. The OBJECT element holding the image must have the SHAPES attribute present. For each active region of the image, you then define an A element nested within the OBJECT element. Each A element contains SHAPE and COORDS attributes, as well as HREF and other applicable link attributes. For nested OBJECT elements, the image map's hotspots can be shared from a nested element to its parent element with the help of the EXPORT attribute, as follows:

<OBJECT data="widget399.pdf" SHAPES>
    <OBJECT data="widget399.gif" SHAPES EXPORT>
    <A HREF="w399Specs.html TARGET="main" SHAPE="rect" COORDS="10,10,40,50">
    <A HREF="w399Price.html TARGET="main" SHAPE="rect" COORDS="40,10,80,50">
    <A HREF="w399Order.html TARGET="main" SHAPE="rect" COORDS="10,50,80,100">
    </OBJECT>
</OBJECT>

The long list of attributes for the OBJECT element attempts to handle every possible data type that may come along in the future. Moreover, content-specific parameters may also be passed via PARAM elements that can go inside the start and end tags of the OBJECT element.

To determine which attributes apply to a particular content type or object and what their values look like, you have to rely on documentation from the supplier of the object or plugin. That same documentation should let you know whether the functionality is available across browser brands and operating systems.

A single character key that brings focus to the element. The browser and operating system determine if the user must press a modifier key (e.g., Ctrl, Alt, or Command) with the access key to bring focus to the element. In IE 4/Windows, the Alt key is required, and the key is not case sensitive. This attribute does not work in IE 4/Mac.

Determines how the rectangle of the OBJECT element aligns within the context of surrounding content. See the section "Alignment Constants" earlier in this chapter for a description of the possibilities defined in both Navigator and Internet Explorer for this attribute. Not all attribute values are valid in browsers prior to the Version 4 releases.

Both browsers follow the same rules on laying out content surrounding an image whose ALIGN attribute is set, but the actual results are sometimes difficult to predict when the surrounding content is complex. A thorough testing of rendering possibilities with browser windows set to various sizes prevents surprises later.

A space-delimited list of URLs of files that support the loading and running of the OBJECT element. By explicitly specifying the files in the ARCHIVE attribute, the browser doesn't have to wait for the supporting files to be called by the content running in the OBJECT element. Instead, the supporting files can be downloaded simultaneously with the primary content. The ARCHIVE attribute may also include URLs assigned to the CLASSID or DATA attributes, but one of these two attributes still needs to point to the primary content URL.

The thickness of a border around the OBJECT element. This attribute is supported in Internet Explorer 3, but not in IE 4. The attribute is also deprecated in HTML 4.0 in favor of style sheet borders.

The URL of the object's implementation. This attribute typically directs the browser to load program, applet, or plugin class files. In Internet Explorer, the URL can point to the CLSID directory that stores all of the IDs for registered ActiveX controls, such as DirectAnimation. You must obtain the CLASSID value from the supplier of an ActiveX control. In Navigator 4, the Java Archive (JAR) Installation Manager attempts to install a plugin from the CLASSID URL if the plugin is not installed for data specified in the DATA attribute. Eventually, this attribute may be used to load Java applets (IE 4 includes a CODE attribute to handle this now), but through Version 4 of both browsers, Java applets are not yet supported in this fashion.

The CODE attribute is likely an interim solution in Internet Explorer that allows the OBJECT element to perform the same job as an APPLET element, using the same kind of attributes. The CODE attribute value is the name of the Java applet class file. If the class file is in a directory other than the document, the path to the directory must be assigned to the CODEBASE attribute, just like in the APPLET element. Eventually, the CODE attribute may be supplanted by the HTML 4.0 CLASSID attribute, which is intended for all object implementations. Parameters are passed to applets via PARAM elements, just like the ones nested inside APPLET elements.

Path to the directory holding the class file designated in either the CODE or CLASSID attribute. The CODEBASE attribute does not name the class file, just the path. You can make this attribute a complete URL to the directory, but don't try to access a codebase outside of the domain of the current document.

An advisory about the content type of the object referred to by the CLASSID attribute. A browser might use this information to assist in preparing support for a resource requiring a multimedia player or plugin. If the CODETYPE attribute is missing, the browser looks next for the TYPE attribute setting (although it is normally associated with content linked by the DATA attribute URL). If both attributes are missing, the browser gets the content type information from the resource as it downloads.

URL of a file containing data for the OBJECT element (as distinguished from the object itself). For data whose content type can be opened (and viewed or played) with any compatible object or plugin, the DATA and TYPE attributes are generally sufficient to launch the plugin and get the content loaded. But if the content requires a very specific plugin or ActiveX control, you should include a CLASSID attribute that points to the object's implementation as well. In that case, you can specify the content type with either the CODETYPE or TYPE attributes. Relative URLs are calculated relative to the CODEBASE attribute, if one is assigned; otherwise the URL is relative to the document's URL.

Used with IE 4 data binding to associate a remote data source column name to an OBJECT element attribute determined by properties set in the object. A DATASRC attribute must also be set for the element.

Used with IE 4 data binding to specify the name of the remote ODBC data source (such as an Oracle or SQL Server database) to be associated with the element. Content from the data source is specified via the DATAFLD attribute.

The presence of the DECLARE attribute instructs the browser to regard the current OBJECT element as a declaration only, without instantiating the object. A browser may use this opportunity to precache data that does not require the object being loaded or run. Another OBJECT element pointing to the same CLASSID and/or DATA attribute values, but without the DECLARE attribute, gets the object running.

If a set of nested OBJECT elements contain images and those images are established as image maps, you can define one set of image maps for a nested OBJECT and share those specifications with the parent OBJECT element by including an EXPORT element.

The size that an embedded object (or its plugin control panel) occupies in a document is governed by the HEIGHT and WIDTH attribute settings. Some browser versions might allow you to get away without assigning these attributes and letting the plugin's own user interface design determine the height and width of its visible rectangle. It is best to specify the exact dimensions of a plugin's control panel or the data (in the case of images) whenever possible (control panels vary with each browser and even between different plugins for the same browser). In some cases, such as Navigator 4 for the Macintosh, the object may not display if you fail to supply enough height on the page. If you assign values that are larger than the actual object or its control panel, the browser reserves that empty space on the page, which could interfere with your intended page design.

A margin that acts as whitespace padding around the visual content of the OBJECT element's rectangular space. HSPACE establishes a margin on the left and right sides of the rectangle; VSPACE establishes a margin on the top and bottom sides of the rectangle.

The HTML 4.0 specification provides for a NAME attribute of the OBJECT element for instances in which the object is part of a form that is submitted to the server. The NAME attribute in this case performs the same function as the NAME attribute of an INPUT element; it acts as a label for some data being submitted. The code that is loaded into the OBJECT element must be programmed to return a value if it is to be submitted via an HTML form.

The presence of the SHAPES attribute instructs the browser to treat the OBJECT element's image as a client-side image map and the nested A elements as hotspot definitions for the map. Nested A elements must include COORDS attribute settings. An OBJECT element can inherit the image map specifications from a nested OBJECT element, provided the nested object specifies both the SHAPES and EXPORT attributes.

HTML content to be displayed while the OBJECT is loading. Although this attribute has not been implemented in Version 4 browsers, presumably the message is to be displayed in the rectangular region intended for the OBJECT element, just as the ALT message appears in an IMG element space while the image loads.

A number that indicates the sequence of this element within the tabbing order of all focusable elements in the document. Tabbing order follows a strict set of rules. Elements that have values other than zero assigned to their TABINDEX attributes are first in line when a user starts tabbing in a page. Focus starts with the element with the lowest TABINDEX value and proceeds in order to the highest value, regardless of physical location on the page or in the document. If two elements have the same TABINDEX values, the element that comes earlier in the document receives focus first. Next come all elements that either don't support the TABINDEX attribute or have the value set to zero. These elements receive focus in the order in which they appear in the document.

An advisory about the content type of the data referred to by the DATA attribute. A browser might use this information to assist in preparing support for a resource requiring a multimedia player or plugin. The DATA element first looks to the CODETYPE attribute for this information. But if the CODETYPE attribute is missing, the browser looks next for the TYPE attribute setting. If both attributes are missing, the browser gets the content type information from the resource as it downloads.

The HTML 4.0 specification lists the USEMAP attribute for an OBJECT element. Because the specification includes another way to associate a client-side image map with an OBJECT element (see the SHAPES attribute), it is unknown at this point if the intention of the USEMAP attribute is for an OBJECT element to be able to point to a named MAP element (as does an IMG element for its client-side image map).