If you have whitespace in a rule, it is internally replaced by a call to the ws token.

The default ws matches at least one space (\s+) if the left and right are word characters (ie matching \w), and matching zero or more (\s*) otherwise.

In code:

class Grammar {
   token ws {
       <!ww> \s*
   }
}
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Where ww is within word, and could be defined as

token ww {
    <after  \w>
    <before \w>
}
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If you want 8.8x5.0 to match, you need to override the ws rule in your grammar:

grammar Calc {
    token ws { \s* }
    # rest of your code here without any modifications
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(Update: fixed ww rule after comment from TimToady++)