Overrides built-in functions by replacing them in the symbol table.
Parameters
function_name
The function to override.
function_args
The function arguments, as a coma separated string.
Usually you will want to pass this parameter, as well as the function_code parameter, as a single quote delimited string. The reason for using single quoted strings, is to protect the variable names from parsing, otherwise, if you use double quotes there will be a need to escape the variable names, e.g. \$your_var.