You'll also enjoy YAPE::Regex::Explain by japhy reading the output of the following snippet:

#!/usr/bin/perl
use strict;
use warnings;
use YAPE::Regex::Explain;
$\ = "\n*************\n";
# Your original
print YAPE::Regex::Explain->new(qr/[a-zA-Z]/)->explain;
print YAPE::Regex::Explain->new(qr/[a-zA-Z]+/)->explain;
print YAPE::Regex::Explain->new(qr/([a-zA-Z]+)/)->explain;
# The solution
print YAPE::Regex::Explain->new(qr/^([a-zA-Z]+)$/)->explain;
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