I like the first approach. The 2nd one is not very flexible, say if you
wanted to add a period or other misc chars.

Just add them to the list. For example... period, comma, equal sign, dash:

Const CharsAllowed = "0-9.,=-"

Another example... is there a Hex digit in the string (upper or lower case
letters permitted):

Const CharsAllowed = "0-9A-Fa-f"

The use of ranges can cut down on typing lots of characters.

Rick