src/Tools/VSCode/extension/README.md

 # Isabelle Prover IDE support
 
-This extension connects to the Isabelle Prover IDE infrastructure, using the
-VSCode Language Server protocol. This requires a recent development version of
-Isabelle from 2017, see also:
+This extension connects VSCode to the Isabelle Prover IDE infrastructure. It
+requires a recent development version of Isabelle from 2017 – one that happens
+to fit to the extension version!
+
+The implementation is centered around the VSCode Language Server protocol, but
+with many add-ons that to VSCode and Isabelle/PIDE.
+
+See also:
 
   * <http://isabelle.in.tum.de/devel/release_snapshot>
   * <http://isabelle.in.tum.de/repos/isabelle/file/tip/src/Tools/VSCode>
 
 ![[Isabelle/VSCode screenshot]](http://isabelle.in.tum.de/repos/isabelle/raw-file/9fe05edaa351/src/Tools/VSCode/extension/isabelle_vscode.png)
 
 
-## Prerequisites ##
+## Notable Features
 
-### Important User Settings ###
+  * Static syntax tables for Isabelle `.thy` and `.ML` files.
 
-  * On Linux and Mac OS X: `isabelle.home` points to the main Isabelle
-    directory (`$ISABELLE_HOME`).
+  * Implicit dependency management of sources, subject to changes of theory
+  files within the editor, as well as external file-system events.
 
-  * On Windows: `isabelle.home` as above, but in Windows path notation with
-    drive-letter and backslashes.
+  * Implicit formal checking of theory files, using the *cursor position* of the
+  active editor panel as indication for relevant spots.
+
+  * Prover messages within the source text (errors/warnings and information
+  messages).
+
+  * Semantic text decorations: colors for free/bound variables, inferred types
+  etc.
+
+  * Visual indication of formal scopes and hyperlinks for formal entities.
+
+  * Implicit proof state output via VSCode message channel ("Isabelle Output").
+
+  * Explicit proof state output via separate GUI panel (command
+  `isabelle.state`).
+
+  * HTML preview via separate GUI panel (command `isabelle.preview`).
+
+  * Rich completion information (similar to Isabelle/jEdit): Isabelle symbols
+  (e.g. `\forall` or `\<forall>`), outer syntax keywords, formal entities,
+  file-system paths, BibTeX entries etc.
+
+  * Spell-checking of informal texts, including dictionary operations: via the
+  regular completion dialog.
 
 
-### Support for Isabelle symbols ###
+## Requirements
 
-Isabelle symbols like `\<forall>` are rendered using the extension "Prettify
-Symbols Mode", which needs to be installed separately.
+### Isabelle Installation
 
-In addition, the following user settings should be changed:
+  * Download a recent Isabelle development snapshot from
+  <http://isabelle.in.tum.de/devel/release_snapshot> or the particular version
+  <http://www4.in.tum.de/~wenzelm/Isabelle_01-Jul-2017>
+
+  * Unpack and run the main Isabelle/jEdit application as usual, to ensure that
+  the logic image is built properly and Isabelle works as expected.
+
+  * Download and install VSCode from <https://code.visualstudio.com>
+
+  * Open the VSCode *Extensions* view and install the following:
+
+      + *Isabelle* (e.g. version 0.20).
+
+      + *Prettify Symbols Mode* (important for display of Isabelle symbols).
+
+      + *bibtexLanguage* (optional): it gives `.bib` a formal status, thus
+        `@{cite}` antiquotations become active for completion and hyperlinks.
+
+  * Open the dialog *Preferences / User settings* and provide the following
+    entries in the second window, where local user additions are stored:
+
+      + On all platforms: `isabelle.home` needs to point to the main Isabelle
+      directory (`$ISABELLE_HOME`).
+
+      + On Windows: use drive-letter and backslashes for `isabelle.home` above.
+      When running from a bare repository clone, `isabelle.cygwin_home` needs to
+      point to a suitable Cygwin installation.
+
+    Examples:
+
+      + Linux:
+        ```
+        "isabelle.home": "/home/makarius/Isabelle_01-Jul-2017"
+        ```
+
+      + Mac OS X:
+        ```
+        "isabelle.home": "/Users/makarius/Isabelle_01-Jul-2017.app/Isabelle"
+        ```
+
+      + Windows:
+        ```
+        "isabelle.home": "C:\\Users\\makarius\\Isabelle_01-Jul-2017"
+        ```
+
+  * Restart the VSCode application to ensure that all extensions are properly
+  initialized and user settings are updated. Afterwards VSCode should know about
+  `.thy` files (Isabelle theories) and `.ML` files (Isabelle/ML modules).
+
+  The Isabelle extension is be initialized on the first opening of some Isabelle
+  file. It requires a few seconds to start up, with a small popup window saying
+  *Welcome to Isabelle*. If that fails, there might be something wrong with the
+  above user settings, or the Isabelle distribution does not fit to the version
+  of the VSCode extension from the Marketplace.
+
+
+### Support for Isabelle symbols
+
+Isabelle symbols like `\<forall>` are rendered using the extension *Prettify
+Symbols Mode*, which needs to be installed separately.
+
+In addition, the following user settings should be changed in the *Preferences /
+User settings* dialog of VSCode:
 
 ```
 "prettifySymbolsMode.substitutions": [
   {
     "language": "isabelle",

     "prettyCursor": "none",
     "substitutions": []
   }]
 ```
 
+Actual symbol replacement tables are provided by the prover process on startup,
+based on the usual `etc/symbols` specifications of the Isabelle installation.
 
-## Further Preferences ##
+
+### Further Preferences
 
   * Preferred Color Theme: `Light+ (default light)`
 
-  * Alternative Color Theme: `Dark+ (default dark)` – with restrictions: some color
-    combinations don't work out properly.
+  * Alternative Color Theme: `Dark+ (default dark)` – with restrictions: some
+  color combinations don't work out properly.
 
   * Recommended changes to default VSCode settings:
 
     ```
     "editor.acceptSuggestionOnEnter": "off",
     "editor.lineNumbers": "off",
     "editor.renderIndentGuides": false,
-    "editor.rulers": [100],
+    "editor.rulers": [80, 100],
     "editor.wordBasedSuggestions": true,
     ```
+
+## Notable Limitations of Isabelle/VSCode
+
+  * Lack of specific support for the `IsabelleText` fonts: these need to be
+  manually installed on the system and configured for VSCode (cf.
+  `$ISABELLE_FONTS` within the Isabelle environment).
+
+    **Note:** As the Isabelle fonts continue to evelove, installed versions need
+    to be updated according to each new Isabelle version.
+
+  * Isabelle symbols are merely an optical illusion: it would be better to make
+    them a first-class Unicode charset as in Isabelle/jEdit.
+
+  * Isabelle symbol abbreviations like "-->" are not accepted by VSCode.
+
+  * Lack of formal editor perspective in VSCode: only the cursor position (with
+  surrounding lines of text) is used.
+
+  * Lack of formal markup in prover messages and popups.
+
+  * Lack of pretty-printing (line breaks) according to window and font
+  dimensions.
+
+  * Lack of GUI panels for Sledgehammer, Query operations etc.