function _getInitialContext(editor, pos) {
        return {
            "editor": editor,
            "pos": pos,
            "token": editor.getTokenAt(pos)
        };
    }
@private
creates a context object
@param {CodeMirror} editor
@param {{ch:{string}, line:{number}} pos
@return {editor:{CodeMirror}, pos:{ch:{string}, line:{number}}, token:{object}}