Description:
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Wishlist: ability to expand variables in an arbitrary string, which does not seem to be possible currently.  (well, not easily, anyway).

Reproduce code:
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$cat = 'calico';
$hat = 'chapeau';
$string = 'The $cat in the $hat.'; //note single quotes
$string = expand_var($string); //this wishlist function
echo $string;


Expected result:
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The calico in the chapeau.