anchor.diff:  [[eql-syntax-strings]]
   ==== Strings
   
  -Strings are enclosed with double quotes (`"`) or single quotes (`'`).
  +Strings are enclosed with double quotes (`"`).
   
   [source,eql]
   ----
   "hello world"
  -"hello world with 'substring'"
  -----
  +----
  +
  +Strings enclosed in single quotes (`'`) are not supported.
   
   [discrete]
   [[eql-syntax-wildcards]]
  
positive.code: |`\t`             | A tab character
  |`\\`             | A backslash (`\`) character
  |`\"`             | A double quote (`"`) character
  |`\'`             | A single quote (`'`) character
  |====
  ====
  
  [discrete]
  [[eql-syntax-raw-strings]]
  
negative.code: `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
  
  