ses-header-line-menu

ses-header-line-menu is a variable defined in `ses.el'.
Its value is

(keymap "SES header row"
	(Set\ current\ row menu-item "Set current row" ses-set-header-row)
	(Unset\ row menu-item "Unset row" ses-unset-header-row :enable
		    (> ses--header-row 0)))

Documentation:
Context menu when mouse-3 is used on the header-line in an SES buffer.