anchor.diff:  
   WARNING: This section is still evolving. Expect changes.
   
  -TODO: Expected behaviors of the `#include` directive.
  -
   If `#include` directives are used in a shader, there will be an `#extension
   GL_GOOGLE_include_directive : enable` line generated into the preprocessed
   output.
  
positive.code: The `GL_GOOGLE_cpp_style_line_directive` extension is implicitly turned on by
  the `GL_GOOGLE_include_directive` extension.
  
  It is invalid to have any '\' or '/' characters in any filename provided to
  an `#include` directive. The presence of any such characters may lead to
  unexpected behavior on different systems.
  
  Furthermore it is not possible to escape any characters in an `#include`
  directive and as such, any special characters that would have to be escaped in
  C may not show up in file names either.
  
negative.code: 
  ==== `-I`
  
  `-Idirectory' or `-I directory` adds the specified directory to the search path
  for include files.  The directory may be an absolute path or a relative path to
  the current working directory.
  
  === Code Generation Options
  
  