Attr.IDPrefix
TYPE: string
VERSION: 1.2.0
DEFAULT: ''
--DESCRIPTION--
String to prefix to IDs.  If you have no idea what IDs your pages may use,
you may opt to simply add a prefix to all user-submitted ID attributes so
that they are still usable, but will not conflict with core page IDs.
Example: setting the directive to 'user_' will result in a user submitted
'foo' to become 'user_foo'  Be sure to set %HTML.EnableAttrID to true
before using this.  
