$SyntaxHandler

• The arguments given to $SyntaxHandler are the complete input string and an integer specifying the character position at which the syntax error was detected.

• The first character in the string is taken to have position 1.

• Any string returned by $SyntaxHandler is used as a new version of the input string, and is fed to Mathematica. If the string does not end with a newline, Mathematica waits for input to complete the line.

• If $SyntaxHandler returns $Failed, input to Mathematica is abandoned if possible.

• Input is not assigned to InString[n] until after $SyntaxHandler is applied.

• $SyntaxHandler is not called for input from files obtained using Get.