The precedence of an operator specifies how "tightly"
it binds two expressions together. For example, in the
expression 1 + 5 * 3, the answer
is 16 and not
18 because the multiplication ("*") operator has a
higher precedence than the addition ("+") operator.
Parentheses may be used to force precedence, if necessary.
For instance: (1 + 5) * 3
evaluates to 18.
The following table lists the precedence of operators
with the lowest-precedence operators listed first.
表格 11-1. Operator Precedence
注: Although ! has a higher precedence than =, PHP will still allow expressions similar to the following: if (!$a = foo()), in which case the output from foo() is put into $a.