Regular Expression: Matching substring

[Leon]

You are right. In fact the procedure is as follows:
The substr ``101101" is no problem, if stop here, match will
successful.
But the tailing `1' occurs, so we may imagine the working automata move
to a state, which according to the regexp's outer most `)', and ready
to repeat
the whole regexp again. In this case, the answer is ``yes" only when
there exists
at least two ``1", but only one here.

BTW, the first string is matched exactly, according to your notion, it
should be written as: _11_0_1011101