anchor.diff:  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.
  +The file argument to `#include` must be enclosed in double quotes.  It must be a
  +relative path, using whatever path separator the OS supports.  However, the last
  +path element -- the name of the file itself -- must not contain either '/' or
  +'\', regardless of which path separator is used.  This will not be flagged as an
  +error but will instead trigger undefined behavior.  For example, let's say there
  +is a file named `f\ilename.vert` on a Unix OS.  It is not possible to craft a
  +`#include` that includes that file.
  +
  +Furthermore, it is not possible to escape any characters in a `#include`
  +directive, so the file argument cannot contain any special characters that need
  +escaping in C.
  +
  +The file argument is a relative path that is matched first against the including
  +file's own directory and then against all `-I` arguments in order of their
  +appearance on the command line.  If the file cannot be found, `glslc` aborts
  +with an error.
  
positive.code: 
  ==== `-I`
  
  `-I` adds the specified directory to the search path for include files.
  
  Only `""` style includes are permitted. When searching for included files, first
  the directory of the current file is attempted. If this fails each directory
  supplied via `-I` on the command line is searched in the given order for the
  file.
  
  === Code Generation Options
  
  
negative.code: 
  WARNING: This section is still evolving. Expect changes.
  
  If `#include` directives are used in a shader, there will be an `#extension
  GL_GOOGLE_include_directive : enable` line generated into the preprocessed
  output.
  