the string "7890" does not yield a
match because only those alternatives that match at one point in the subject
are remembered. The problem arises because the start of the second alternative
matches within the first alternative. There is no problem with anchored
patterns or patterns such as:
<pre>
  1234|ABCD
</pre>
where no string can be a partial match for both alternatives. This is not a
problem if a standard matching function is used, because the entire match has
to be rerun each time:
<pre>
    re&#62;