2.1.1 ?IMPORT?
Quirks Mode, IE7 Mode, IE8 Mode, and IE9 Mode (All Versions)
A processing instruction that imports a tag definition from an element behavior. Two attributes are required:
The value of an XMLNS attribute that has been defined in the HTML tag must correspond to the value of the namespace attribute defined in the IMPORT processing instruction (PI). Otherwise, the imported tag definition cannot be used.
An imported tag will not render if the value of the implementation attribute is not valid. When using an HTC file, the file must comply with the same security rules as all behaviors. For more information, see Introduction to DHTML Behaviors [MSDN-DHTMLBehaviors].
The IMPORT PI must be placed before the first instance of a custom element that uses the imported tag definition. If the IMPORT PI is placed after the custom element, the behavior does not attach to the custom element. This also means that the document.write method should not be used to add the IMPORT PI to a document.
The IMPORT PI is only processed during the initial parsing of the document. Therefore, a document that uses an element behavior must include the IMPORT PI in the HTML file. Provided that the IMPORT PI is specified in the primary document, the document.write method can be used to add the custom element and attach to the behavior.