anchor.diff:  `nested` field mappings are otherwise supported.
   
   [discrete]
  +[[single-quote-strings]]
  +==== Single quote strings
  +
  +In {es} EQL, the single quote (`'`) character is reserved for future use. 
  +Strings enclosed in single quotes are not supported. Enclose strings in
  +double quotes (`"`) instead.
  +
  +You cannot use an escaped single quote (`\'`) for literal strings. Use an
  +escaped double quote (`\"`) instead. 
  +
  +[discrete]
   [[eql-unsupported-syntax]]
   ==== Unsupported syntax
   
  
positive.code: |`\t`             | A tab character
  |`\\`             | A backslash (`\`) character
  |`\"`             | A double quote (`"`) character
  |`\'`             | A single quote (`'`) character
  |====
  ====
  
  [discrete]
  [[eql-syntax-raw-strings]]
  
negative.code: 
  [source,eql]
  ----
  ?"String with a literal blackslash \ character included"
  ----
  
  You can escape double quotes (`"`) with a backslash, but the backslash remains
  in the resulting string.
  
  [source,eql]
  ----
  