title: does mXparser support string compare and substring built in function?
body: <p>I'm using mXparser to evaluate expressions. Now i need support for string compare and sub-string<br>
  built in function. i can't find anything about strings in the documentation.
  what i need is something like the substring in the below function</p>
  
  <p>isOfCategoryX ( SKU, X ) = if ( substring(SKU,3,2) = X , 1 , 0 )</p>