When multiple XTREE controls are in simultaneous use, specifies which one (range is 0 to 31) to use for this call. If XTR_OPCODE = XTROP_CREATE, you can set XTR.CTLNO to –1 to have XTREE automatically assign the next available control number. If the control is modeless, you will need to save the returned XTR.CTLNO value for referencing it in subsequent calls.
Note: XTR.CTLNO enumerates/identifies only the XTREE controls, using a numbering scheme only meaningful to XTREE. See XTR.CTLID for the standard control ID (which can be specified in the AUI_CONTROL ctlid parameter) to perform standard control operations on the XTREE control such as hide, move, etc.
Here is an illustration of multiple XTREEs on the screen at once, for which you absolutely need to keep unique XTR.CTLNO values.
