Positional anchors can be constructed using patterns. These are enclosed in grouping operators and commence with a question mark.
A positional anchor, marking the location immediately before a capital letter would look like this:
A positional anchor marking a location immediately before any non-capital letter would look like this:
The second example uses the logical negation operator.
Note that these are positional anchors that behave like the ^ and $ which denote the start and end of a line. They do not select any characters.
ECMA 262 edition 3 - section - 15.10.1
ECMA 262 edition 3 - section - 18.104.22.168
ECMA 262 edition 3 - section - 22.214.171.124