Expand replaces Widen: fill the window in both directions

From the development repository at 3f1da52.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

docs/guest.md

@@ -153,11 +153,11 @@ two gestures change the view, and none of them changes the page:
 * When the host presses **Fit** or **A4**, every participant's view
   follows, each in their own window.  Your own Fit and A4 change only
   your screen.
-* **Widen**, which only the host and co-hosts have, makes the page
-  itself wider, for everyone, until it fills the
-  window at the present zoom.  The sheet grows equally on both sides,
-  so nothing on the page moves and nothing is rescaled; there is simply
-  more room at either side.
+* **Expand**, which only the host and co-hosts have, makes the page
+  itself fill the window, for everyone, at the present zoom, in both
+  directions.  The sheet grows equally on every side, so nothing on the
+  page moves and nothing is rescaled; there is simply more room around
+  it.
 * **Shrink**, also for the host and co-hosts, makes the page, for everyone, just large enough for what is on it,
   with the usual margin around.  Nothing on it moves either.
 * **Extend** is a box, ticked to begin with.  Ticked, the sheet grows

docs/host.md

@@ -225,10 +225,10 @@ is the "write your answer here" box of a worksheet: draw it on the scan
 where the answer belongs, and the student types into their own box or
 beside yours.  Only its owner can type in a box, as with any text.
 
-**Widen**, among the view buttons, makes the page wider for everyone,
-until it fills your window at your present zoom: the quickest way to
-more room for writing beside an exercise.  The sheet grows equally on
-both sides, so nothing on the page moves.  The page keeps the new width
+**Expand**, among the view buttons, makes the page fill your window for
+everyone, at your present zoom, in both directions: the quickest way to
+more room for writing around an exercise.  The sheet grows equally on
+every side, so nothing on the page moves.  The page keeps the new size
 in everyone's notebook.  **Shrink** is its opposite: the page becomes
 just large enough for everything on it, images and writing, with the
 margin of 5 mm around, which trims a page down to its exercise before you keep
@@ -266,7 +266,7 @@ notebook in the toolbar first.
 In the **Participants** list of the Session window, each guest's name
 has a box **Co-host** beside it.  Ticking it makes that guest a
 co-host: they may then start new pages, put images on the page and
-arrange them, load pages from their notebook, widen, shrink and hide,
+arrange them, load pages from their notebook, expand, shrink and hide,
 exactly as you can, and the buttons for it appear on their toolbar.
 Unticking it takes it back; otherwise it lasts until the session
 ends.  What stays yours alone: making co-hosts, and bringing everyone's

docs/implementation.md

@@ -113,7 +113,8 @@ from the host (or from an allowed guest, for pages and images).
 ## Pages
 
 Page coordinates are in units of 0.1 mm.  A blank page is an A4 sheet
-in landscape, 2970 by 2100 units.  "Widen" makes the sheet wider, and
+in landscape, 2970 by 2100 units.  "Expand" makes the sheet fill the
+window in both directions, and
 "Shrink" makes it the bounding box of everything on the page plus the
 greater of the two margins, exactly, on every side; both are changes to the page like adding
 an image, carried in the page descriptor (its `left` and `top` edges and

docs/quickstart.md

@@ -68,7 +68,7 @@ rather than in the browser's storage.
 ## The screen in one paragraph
 
 The toolbar holds the pen, text, eraser and hide tools, colours and
-line widths, the view commands (Fit, A4, Widen, Shrink, Extend), the
+line widths, the view commands (Fit, A4, Expand, Shrink, Extend), the
 host's page buttons (New, Image, Notebooks), your notebook, Keep, Export
 and Session.  Rest the pointer on any button for a second for its
 explanation.  Each participant writes on a layer of their own that