Show what the content of the gallery, tree and menu macros accepts in the WYSIWYG editor

The gallery, tree and menu macros only use part of what their content can hold: images for the gallery, nested lists for the tree and the menu. The WYSIWYG editor lets the user put anything in their content, such as a table or a box, and shows it there, but the macros silently drop it or show it as is in view mode, with no message. The user only finds out after saving.

The macros to change, with the file where most of the fix is done:

• gallery: GalleryMacro.java.
• tree: Tree.xml.
• menu: MenuMacro.xml.

The main problems:

• The editor offers every editing feature inside the content, while only images or lists are used: unsupported content can be inserted or pasted with no notification.
• The unsupported content is shown in the editor but dropped or misplaced in view mode, so the editor and view mode disagree.
• The content description of the tree speaks of nested HTML unordered lists and links to the jstree documentation, while users type wiki lists in the WYSIWYG editor.

The improvement is to make the restriction visible, as the gallery and menu descriptions already state it: disable the unsupported features inside the content, notify the user when unsupported content is pasted, and, in view mode, report the content that is ignored instead of dropping it silently.

KOs covered

Impact found on macro fluidity

These 3 KOs come from the WYSIWYG usability audit of the macros, under the criterion E3 nesting of its usability criteria, which asks that when the macro content accepts less than the rest of the page, the restriction is visible. The page of each macro, linked in the table, has the full notes and the steps to reproduce. The other part of the E3 KOs of gallery, tree and menu, their error in a list item or a table cell, is XWIKI-23501.