Well, there would be no point making two test if the result of one was the subset of the other (for exemple "a value that is positive and greater than 10"). In Perl, this condition would actually be: $matches if $_ ne '' and /^[a-zA-Z]*[0-9]*\z/ this was probably to have something easier to understand than one of those two patterns:

/^(?:
   [a-zA-Z]+ [0-9]*
   |
   [a-zA-Z]* [0-9]+
  )
\z/x;

/^(?=.)[a-zA-Z]*[0-9]*\z/;
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The first one being a bit long, and the second not so beginner friendly.