Check Table Values.

While going through this standard SAP program 'BCALV_GRID_EDIT'. I came through this interesting piece of code for populating field catalog of an OO ALV.

<b>clear gs_fieldcat.

gs_fieldcat-fieldname = 'CURRENCY'.

gs_fieldcat-ref_table = 'SFLIGHT'.

gs_fieldcat-edit = 'X'.

gs_fieldcat-checktable = '!'.

gs_fieldcat-auto_value = 'X'.

append gs_fieldcat to gt_fieldcat.</b>Can Somebody please explain me the use of this EXCLAIMATION MARK ⚠️, in the checktable value in details?