/usr/share/metview/etc/UiSpec.Bookmarks is in metview-data 4.8.0-4.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
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# Icon context menu
#------------------------------------
icon_menu,
	cmd		   = open,
	label		   = 'Open',
        condition          = 'path!=FOLDERGROUP'
icon_menu,
	cmd		   = openInTab,
	label		   = 'Open in new tab',
        condition          = 'path!=FOLDERGROUP'
icon_menu,
	cmd		   = openInWin,
	label		   = 'Open in new window',
        condition          = 'path!=FOLDERGROUP'
icon_menu,
	cmd		   = openGroup,
	label		   = 'Open tabs',
        condition          = 'path=FOLDERGROUP'
icon_menu,
	cmd		   = openGroupInWin,
	label		   = 'Open tabs in new window',
        condition          = 'path=FOLDERGROUP'
icon_menu,
	type 		   = separator
icon_menu,
	cmd		   = editEntry,
	label		   = '&Properties',
	shortcut	   = Ctrl+E,
        icon 		   = edit
	
icon_menu,
	cmd		   = duplicateEntry,
	label		   = '&Duplicate',
	shortcut	   = Ctrl+D,
        icon 		   = duplicate
icon_menu,
        cmd		   = removeEntry,
	label		   = '&Remove',
	shortcut	   = Del,
        icon 		   = remove
	
icon_menu,
	type 		   = separator
icon_menu,
        cmd		   = empty,
	label		   = 'Empty &wastebasket',
        shortcut           = 'Ctrl+W',
	condition	   = 'path=wastebasket'
#------------------------------------
# Desktop context menu
#------------------------------------
desktop_menu,
	cmd		   = addEntry,
	label		   = 'Bookmark current folder',
        icon               = 'add_bookmark'
desktop_menu,
	cmd		   = addTabs,
	label		   = 'Bookmark current tabs',
        icon               = 'add_bookmark_group'
desktop_menu,
	type 		   = separator
 
desktop_menu,
	cmd		   = addBookmark,
	label		   = '&New bookmark',
        icon               = 'add'
desktop_menu,
	type 		   = separator
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