You haven't told your regex to match the entire string, so it will "pass"
any string that has your match anywhere within it, so like as long as it's
got an R or a digit in it: it's OK.
To tell it to match the entire string, anchor it to the start and end of the
string with ^ and $ respectively.
Regular expression syntax: Using special characters
Your regex is basically correct. All you need to do is to say "and make
sure it matches the entire string", not just "any substring", like you
To do this, one forces the regex to match from the beginning of the string,
right through to the end of the string.
So, for example a regex of "ant" would match "ant" or "pants" or
"elephant". However "^ant$" would not match "pants" or "elephant" because
the "^" means "match the beginning of the string", and "$" means "match the
end of the string". In effect this makes it so your regex must match the