(SKEEP(source, chars))
Keeps characters within the source string, using chars as a comparison.
This function is CASE SENSITIVE.
In the following example, the value of vskeep is ldilliamennighway.
SET VAR vskeep = (SKEEP('3935 Old William Penn Highway','abcdefghijklmnopqrstuvwxyz'))
Spaces are also recognized.
In the following example, the value of vskeep2 is ld illiam enn ighway.
SET VAR vskeep2 = (SKEEP('3935 Old William Penn Highway',' abcdefghijklmnopqrstuvwxyz'))
