function hintableKey(key, showOnDot) {
        return (key === null || (showOnDot && key === ".") || maybeIdentifier(key));
    }
Determine if hints should be displayed for the given key.

@param {string} key - key entered by the user
@param {boolean} showOnDot - show hints on dot (".").
@return {boolean} true if the hints should be shown for the key,
false otherwise.