Fix diagram navigation and token highlighting

README.md

@@ -187,11 +187,22 @@ opens it for you. It is a local web app that edits **real files on disk**:
   listed under *Problems*; ANTLR tool errors are marked in the grammar at the
   reported line. Click a problem to jump to it. Hovering or clicking a node in
   the diagram, or a row in *Tokens*, highlights its text in the input.
-- **Diagram** with zoom (wheel), pan (drag), *Fit*, and SVG / PNG export. *Tree*
-  shows the LISP form (indented or on one line, with Copy), *Tokens* the token
-  table.
-- **Editor niceties:** grammar syntax colors, line numbers, auto-indent,
-  `Tab` / `Shift+Tab` indent, `Ctrl+/` comment, `Ctrl+F` find and replace.
+- **Diagram** with zoom (wheel, `+` / `-`), pan (drag; it never selects text),
+  *Fit* (double-click or `0`), and SVG / PNG export. **Click or select text in
+  the input** and the diagram glides to the matching node (the smallest one that
+  covers the text, a token rather than a rule when both match) and outlines it.
+  *Tree* shows the LISP form (indented or on one line, with Copy), *Tokens* the
+  token table.
+- **Editor niceties:** grammar syntax colors, line numbers, `Ctrl+/` comment,
+  `Ctrl+F` find and replace, and indentation with **hard tabs** (shown 4 columns
+  wide; `Tab` / `Shift+Tab` also indent and outdent a selection). A line that is
+  already indented with spaces keeps getting spaces, so a line never mixes both.
+  `Enter` auto-indents: it keeps the current indentation, adds a level after
+  `(` `[` `{`, and between a pair like `{|}` opens a block with the closer on its
+  own line. In grammars it also indents after a rule name or a `:`, and starts
+  the next line at column 0 after the `;` that ends a rule. A whitespace-only
+  line is emptied when you press `Enter` on it, and typing `}` `)` or `]` first
+  on an indented line steps it back one level.
 - Panels close with their `x` and come back from the View menu; the splitters
   drag. Layout, theme (system / light / dark) and text size are remembered, and
   so are the open files per workspace.
@@ -223,6 +234,10 @@ Opening a file larger than 5 MB or an input larger than 4 MB is refused.
 
 ### Changing the UI
 
+The wheel zoom speed is the `ZOOM` object near the top of the diagram code in
+`web/40-views.js` (`wheel` is the rate per scrolled pixel, `maxStep` caps the
+change of one event).
+
 The browser code lives in `web/` (plain HTML, CSS and JavaScript, no build
 tools or libraries). After editing it, run `python3 tools/embed_web.py` to
 regenerate `src/webui_assets.hpp`, which is checked in, so building antlrlab