Precedence in regular expressions
This depends entirely on convention; with respect to a (proper) formal definition, the expression is invalid as it not properly parenthesised. I'd say that typically, the order is (from stronger to weaker binding)


Kleene Star/Plus (also finite versions),
concatenation,
alternative.


Note that this corresponds (visually) to exponentiation over multiplication over addition in basic arithmetics, so it's probably the natural way.

That is,


$10^*1$ is read as $1(0)^*1$ and
$10|01|11$ as $(10)|(01)|(11)$.


Note that I still drop parentheses due to associativity of concatenation and alternative.