[SDPhantom]

Here's the OnClick handler on PTR.

function SecureActionButton_OnClick(self, inputButton, down, isKeyPress)
    local pressAndHoldAction = SecureButton_GetAttribute(self, "pressAndHoldAction");
    local useOnKeyDown = GetCVarBool("ActionButtonUseKeyDown") or pressAndHoldAction;
    local clickAction = (down and useOnKeyDown) or (not down and not useOnKeyDown);
    local releasePressAndHoldAction = (not down) and (pressAndHoldAction or GetCVarBool("ActionButtonUseKeyHeldSpell"));
 
    if clickAction then
        OnActionButtonClick(self, inputButton, down, isKeyPress);
        return true;
    elseif releasePressAndHoldAction then
        OnActionButtonPressAndHoldRelease(self, inputButton, isKeyPress);
        return true;
    end
 
    return false;
end

-FrameXML\SecureTemplates.lua:730

Basically, the handler is looking for either an up or down click event specifically according to how the ActionButtonUseKeyDown CVar is set. If it never gets the matching click event, the code never runs. It's probably a good idea to register both up and down click events for every button you intend to respond to. If you don't care about registering individual buttons, you can use "AnyUp" and "AnyDown".

Originally Posted by Zax the real macro is something like "/wm 1" or "/cwm 1" to place or clear ground markers.

This code clip may be of interest to you.

SECURE_ACTIONS.worldmarker =
    function(self, unit, button)
        local marker = tonumber(SecureButton_GetModifiedAttribute(self, "marker", button));
        local action = SecureButton_GetModifiedAttribute(self, "action", button) or "toggle";
        if ( action == "set" ) then
            PlaceRaidMarker(marker or 1);
        elseif ( action == "clear" ) then
            ClearRaidMarker(marker);
        elseif ( action == "toggle" ) then
            marker = marker or 1;
            if ( IsRaidMarkerActive(marker) ) then
                ClearRaidMarker(marker);
            else
                PlaceRaidMarker(marker);
            end
        end
    end;

-FrameXML\SecureTemplates.lua:589

This defines type "worldmarker" with parameters "marker" and "action".
As with any other attribute fetched by SecureButton_GetModifiedAttribute(), you can append the attribute name (not the value) with a number representing the mouse button to bind to (1=Left, 2=Right, 3=Middle, etc.)