does not need to be timed to the input more than through a few frames.
This, and the fact that the theme can not present a very detailed UI
-(short of :ref:`simple menus <menu>`), means that it can be hard to
+(short of :ref:`simple menus <menus>`), means that it can be hard to
exert detailed control over the graphics using Nageru alone—you will
probably want to have the theme contact some non-Nageru backend (possibly over
WebSockets) from where it can take detailed instructions.
a restart. (If the file contains an error, the update will be ignored.)
This allows you to e.g. have simple message overlays that you can change
without restarting Nageru.
+
+
+.. _menus:
+
+Theme menus
+-----------
+
+Complicated themes, especially those dealing with `HTML inputs <html>`,
+may have needs for user control that go beyond those of transition buttons.
+(An obvious example may be “reload the HTML file”.) For this reason,
+themes can also set simple *theme menus*, which are always visible
+no matter what inputs are chosen.
+
+If a theme chooses to set a theme menu, it will be available on the
+main menu bar under “Theme”; if not, it will be hidden. You can set
+the menu at startup or at any other point, using a simple series of
+labels and function references::
+
+ function modify_aspect()
+ -- Your code goes here.
+ end
+
+ function reload_html()
+ html_input:reload()
+ end
+
+ ThemeMenu.set(
+ { "Change &aspect", modify_aspect },
+ { "&Reload overlay", reload_html }
+ )
+
+When the user chooses a menu entry, the given Lua function will
+automatically be called. There are no arguments nor return values.
+
+There currently is no support for checkboxes, submenus, input boxes
+or the likes. However, do note that since the theme is written in unrestricted
+Lua, so you can use e.g. `lua-http <https://github.com/daurnimator/lua-http>`_
+to listen for external connections and accept more complicated inputs
+from those.
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