The offset in source where the error was detected.
A zero-based offset into the source that marks the format error causing
this exception to be created. If
source is a string, this should be a
string index in the range
0 <= offset <= source.length.
If input is a string, the toString method may represent this offset as a line and character position. The offset should be inside the string, or at the end of the string.
May be omitted. If present, source should also be present if possible.