I'm playing lately with an XSL-FO for generating a pdf documents.
XSL-FO has a long list of available tags and attributes, which for a new guy who want to create a simple document is a nightmare to find a proper one.
Fortunatelly we can set an schema for XSL-FO, so will result in acquire a full intellisense in VS.

For a simple *.fo file, we can set the path to the schema directly in file:

<?xml version="1.0" encoding="utf-8"?>

<fo:root

      xmlns:fo="http://www.w3.org/1999/XSL/Format"

      xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"

      xsi:schemaLocation="

http://www.w3.org/1999/XSL/Format

http://www.xmlblueprint.com/documents/fop.xsd">

...

We can of course use the build in VS XML Schemas selector. To use it, we must copy the schema file to the Schemas catalog (defaut path for VS2012 is C:\Program Files (x86)\Microsoft Visual Studio 11.0\Xml\Schemas).

Then we can go to Properties of the opened xml/xslt file and set the new added schema to file:

From now, we should have an enable intellisense as shown below:

.