A Gesture Spec with modifiers or data which is not an integer cannot be converted to a character. When supplied such a Gesture Spec,
gesture-spec-to-character either signals an error (if errorp is true), or returns
nil (if errorp is
nil). The default value of errorp is
gesture-spec-accelerator-bit is ignored.
In LispWorks 6.1 and earlier versions,
gesture-spec-to-character allows modifiers and does not error when the data is not an integer. LispWorks 7.0 and later versions do not support character bits, therefore if gspec contains non-zero modifier bits,
gesture-spec-to-character signals an error.
LispWorks User Guide and Reference Manual - 20 Sep 2017