anchor.diff:  *Return Type*: [.returnType]#Boolean#
   
   *Examples*:	`${filename:isNull()}` returns `true` if the "filename" attribute does not exist. 
  -	It returns `true` if the attribute exists.
  +	It returns `false` if the attribute exists.
   
   
   
  
positive.code: | `${filename:substringBefore('.')}` | `a brand new filename`
  | `${filename:substringBefore(' ')}` | `a`
  | `${filename:substringBefore(' n')}` | `a brand`
  | `${filename:sbustringBefore('missing')}` | `a brand new filename.txt`
  |======================================================================
  
  
  
negative.code: manipulation, such as the `toUpper` function. Others, such as the `equals` and `matches` functions,
  provide comparison functionality. Functions also exist for manipulating dates and times and
  for performing mathematical operations. Each of these functions is described below, in the
  <<functions>> section, with an explanation of what the function does, the arguments that it 
  requires, and the type of information that it returns.
  
  When we perform a function call on an attribute, as above, we refer to the attribute as the
  