Moves backward to the next toggle (on or off) of the TextTag
tag, or to the
next toggle of any tag if
tag is null.
If no matching tag toggles are found, returns false, otherwise true. Does not return toggles located at this, only toggles before this. Sets this to the location of the toggle, or the start of the buffer if no toggle is found.
a TextTag, or null
whether we found a tag toggle before this