SAK-13492 has details of how the kernel can filter served up content.
This is useful initially to add headers and footers to HTML fragments created by the FCKEditor in resources.
Centralize JS/CSS HTML head creation
HTML page filter doesn't pickup skin from site containing the content.
can't edit a full web page in CKeditor
Update content filtering to support ranged GETs
In Resources: "Create HTML page" only actually creates a page fragment