Expand/collapse buttons are optional buttons displayed to allow users to expand and collapse tree sections by clicking a button. The button graphics can be modified and are shared between all items (see SetButtons). Items on level 0 (the highest level or ) have special level 0 expand/collapse buttons which can be enabled separately, but share the same graphics.
Expand/collapse buttons are enabled using SetShowButtons and SetShowButton0. The location of an expand/collapse button can be determined using the GetExpandCollapseButtonRect function.
Expand/collapse buttons for individual items can be suppressed using the SetItemExpandCollapseButton function.