String quote handling

[berland]

This cannot be parsed:

rms:
  COHIBA: "ON" ~ <>

as it gives a yaml.parser.ParserError: while parsing a block mapping

This works fine:

rms:
  COHIBA: ON ~ <>

and is probably the canonical way to do it, but yaml will let this pass with no problems:

rms:
  COHIBA: "ON"

which can create confusion.

[jcrivenaes]

This is difficult to fix with the current implementation.

A possible solution would be to "pre-parse" the YAML files and split into two files (or streams) before actual YAML parsing. One with actual value and one with template values.

Side note: The YAML parser evaluates "ON" to True, not to the string "ON"