anchor.diff:  
   [[expressions-ref-literal]]
   === Literal expressions
  -The types of literal expressions supported are strings, dates, numeric values (int,
  -real, and hex), boolean and null. Strings are delimited by single quotes. To put a
  -single quote itself in a string use two single quote characters. The following listing
  -shows simple usage of literals. Typically they would not be used in isolation like this,
  -but as part of a more complex expression, for example using a literal on one side of a
  -logical comparison operator.
  +The types of literal expressions supported are strings, numeric values (int, real, hex),
  +boolean and null. Strings are delimited by single quotes. To put a single quote itself
  +in a string, use two single quote characters.
  +
  +The following listing shows simple usage of literals. Typically they would not be used
  +in isolation like this but rather as part of a more complex expression, for example
  +using a literal on one side of a logical comparison operator.
   
   [source,java,indent=0]
   [subs="verbatim,quotes"]
  
positive.code: evaluation context, root object and any predefined variables are all set up implicitly,
  requiring the user to specify nothing other than the expressions.
  ====
  As a final introductory example, the use of a boolean operator is shown using the
  Inventor object in the previous example.
  
  
negative.code: 	// evaluates to true
  	boolean trueValue = parser.parseExpression("'black' < 'block'").getValue(Boolean.class);
  ----
  
  [NOTE]
  ====
  Greater/less-than comparisons against `null` follow a simple rule: `null` is treated as
  nothing here (i.e. NOT as zero). As a consequence, any other value is always greater
  than `null` (`X > null` is always `true`) and no other value is ever less than nothing
  (`X < null` is always `false`).
  
  If you prefer numeric comparisons instead, please avoid number-based `null` comparisons
  in favor of comparisons against zero (e.g. `X > 0` or `X < 0`).
  ====
  
  In addition to standard relational operators SpEL supports the `instanceof` and regular
  expression based `matches` operator.
  