https://docs.dopus.com/doku.php?id=reference:command_reference:command_modifier_reference
@hideif The button will be hidden if a command clause test is false. This is similar to the conditional testing offered by the @if modifier described below.
@hideif:Set DUAL=toggle button will be hidden if the Lister is in dual-display mode
@hideif:!Set DUAL=toggle button will be hidden if the Lister is NOT in dual-display mode
If I understand, the button will be hidden if a command clause test is true (no if is false).