Get the substring at the position and length: identical to the built in Mid function. Returns an error if the StartPosition is beyond the string end. See SafeMid for a fault tolerant version.
The string to search
The start position of the substring
The number of characters to return, or -1 for the rest of the string
1 2 | xf.Str.SubString( "The King's counting house" , 12) => counting house xf.Str.SubString( "The King's counting house" , 12, 5) => count |