PatternTest

pat?test matches when the expression matches pat and test[MATCH] evaluates to True.

Attributes[PatternTest] := {HoldRest, Protected}

Simple examples

In[1]:= MatchQ[1, PatternTest[_, NumberQ]]
Out[1]= True

In[2]:= MatchQ[a, PatternTest[_, NumberQ]]
Out[2]= False

In[3]:= MatchQ[1, PatternTest[1, NumberQ]]
Out[3]= True

In[4]:= MatchQ[1, PatternTest[1.5, NumberQ]]
Out[4]= False

In[5]:= MatchQ[1.5, PatternTest[1.5, NumberQ]]
Out[5]= True

In[6]:= Cases[{5, 2, a^b, x, y, 4.5}, PatternTest[_, NumberQ]]
Out[6]= {5, 2, 4.5}