Syntax: is_member (ANY value, LIST list, INT case-sensitive) => INT
Returns the index of <value> if there is an element of <list> that is completely indistinguishable from <value>. This is much the same operation as "<value> in <list>" except that, unlike `in', the `is_member()' function does not treat upper- and lower-case characters in strings as equal. This treatment of strings can be controlled with the <case-sensitive> argument; setting <case-sensitive> to false will effectively disable this behavior.
Raises E_ARGS if two values are given or if more than three arguments are given. Raises E_TYPE if the second argument is not a list. Otherwise returns the index of <value> in <list>, or 0 if it's not in there.