<sources> element has the following errors:
1. Typo in Concepts "auser".
2. Typo in Child Elements "apper".
3. Intro sentence is confusing, says "Concatenates the source code for a shader from one or more sources." Change to "Creates shader source code by concatenating code from one or more sources.
4.Concepts says "Sometimes shader source code cannot be contained in only one included file or one embedded code block". Change to "Sometimes shader source code cannot be contained in a single included file or in a single embedded code block."
5. Child element <inline> says occurs 1 or more times; per schema, 0 or more.
6. Child element descriptions aren't phrased as verbs like everything else in the document.
7. Description of <import> child redundantly states "the required ref attribute...The ref attribute is required."