Mapping L_ALT + LEFT ARROW to BackSpace with X11 and xkb

Question

I would love to bind left left alt + ← to backspace with XKB (edit: I mean, when I click left alt + left arrow, I want it to behave like backspace).

I have this in my /usr/share/X11/xkb/symbols/pc file, along with my changes:

hidden partial alphanumeric_keys
xkb_symbols "editing" {
    key <PRSC> {
    type= "PC_ALT_LEVEL2",
    symbols[Group1]= [ Print, Sys_Req ]
    };
    key <SCLK> {    [  Scroll_Lock      ]   };
    key <PAUS> {
    type= "PC_CONTROL_LEVEL2",
    symbols[Group1]= [ Pause, Break ]
    };
    key  <INS> {    [  Insert       ]   };
    key <HOME> {    [  Home         ]   };
    key <PGUP> {    [  Prior        ]   };
    key <DELE> {    [  Delete       ]   };
    key  <END> {    [  End          ]   };
    key <PGDN> {    [  Next         ]   };

    key   <UP> {    [  Up           ]   };

    //THIS IS MY MODIFICATION, it used to be just Left :

    key <LEFT> {    [  Left,Left, BackSpace         ]   };
    key <DOWN> {    [  Down         ]   };
    key <RGHT> {    [  Right        ]   };
};

But it doesn't work for two reasons, first - it seems to react to only the RIGHT alt key and.. that is what I expected actually. Second - even in this case it doesn't really work in every app, because some of them receive this: user pressed right alt, and then backspace.

I would love to bind LEFT Alt + LEFT Arrow to simply BACKSPACE.

BTW, this is very similar to this question, which has no answer since 2014, really it is not possible?

Bind ALT + Left/Right arrow to HOME and END keys in XKB