write the environment variables page and drop cli options

docs/reference/environment-variables.md

@@ -2,8 +2,134 @@
 title: Environment Variables
 ---
 
-Environment variables that trigger and configure debug sessions at runtime, overriding php.ini settings.
+Environment variables let you configure the debugger for a single command without
+touching `php.ini` — which is what makes them the natural fit for a container, a CI
+job, or a one-off run from your shell.
+
+They are listed here in alphabetical order.
+
+## `PHP_DEBUGGER_CONFIG`
+
+Sets configuration values for this run. The value is a space-separated list of
+`key=value` pairs, with the keys written without their `php_debugger.` prefix:
+
+```bash
+PHP_DEBUGGER_CONFIG="client_host=192.168.1.10 client_port=9004" php your-script.php
+```
+
+Only these keys are accepted:
+
+| Key | |
+| --- | --- |
+| `client_host` | Where to connect |
+| `client_port` | Which port |
+| `discover_client_host` | Work the address out from the request |
+| `cloud_id` | Relay through Xdebug Cloud |
+| `idekey` | Session identifier |
+| `log` | Where to write the debug log |
+| `log_level` | How much to write |
+| `on_demand_debugging_enabled` | Allow attaching mid-request |
+
+Anything else in the list is ignored. Each key behaves exactly as the
+[setting](./settings.md) of the same name.
+
+## `PHP_DEBUGGER_IGNORE`
+
+Stops the debugger activating for this request, whatever else is configured.
+
+```bash
+PHP_DEBUGGER_IGNORE=1 php ./bin/console cache:clear
+```
+
+Any value ignores the request except `no` and `0`, which explicitly do not. It is
+the quickest way to keep one command out of a debugging session — a build step or a
+cache warm-up you would rather not step through.
+
+## `PHP_DEBUGGER_MODE`
+
+Overrides [`php_debugger.mode`](./settings.md#php_debuggermode) for this run, which
+is otherwise settable only in `php.ini`.
+
+```bash
+PHP_DEBUGGER_MODE=off php benchmark.php
+```
+
+This is the one way to turn the debugger off for a single command without editing
+configuration. An unrecognised value is reported and the `php.ini` setting is used
+instead.
+
+## `PHP_DEBUGGER_SESSION`
+
+An older name for `PHP_DEBUGGER_TRIGGER`, still honoured. It is only consulted when
+no trigger variable was found, so prefer the trigger name in anything new.
+
+## `PHP_DEBUGGER_SESSION_START`
+
+Starts a debugging session for this run, taking the value you give it as the
+session's identifier:
+
+```bash
+PHP_DEBUGGER_SESSION_START=my-session php your-script.php
+```
+
+Over HTTP it does one thing more: alongside starting the session it sets a cookie,
+so the requests that follow in the same browser keep debugging without the variable
+being present each time.
+
+```
+https://example.test/page.php?PHP_DEBUGGER_SESSION_START=1
+```
+
+That cookie is what distinguishes it from a plain trigger: a trigger applies to the
+request carrying it, whereas this persists across the ones that follow.
+
+## `PHP_DEBUGGER_TRIGGER`
+
+Starts a session when
+[`php_debugger.start_with_request`](./settings.md#php_debuggerstart_with_request)
+is set to `trigger`. With the default of `yes` it is not needed, because every
+request already starts one.
+
+```bash
+PHP_DEBUGGER_TRIGGER=1 php your-script.php
+```
+
+Any value will do unless
+[`php_debugger.trigger_value`](./settings.md#php_debuggertrigger_value) is set, in
+which case the value has to match one of the configured secrets.
+
+:::info[Triggers are not only environment variables]
+
+`PHP_DEBUGGER_TRIGGER`, `PHP_DEBUGGER_SESSION` and `PHP_DEBUGGER_SESSION_START` are
+each looked for in `$_GET`, then `$_POST`, then `$_COOKIE`, and only then in the
+environment — so a query parameter of the same name wins over the environment, not
+the other way round.
+
+That is what makes them usable from a browser as well as a shell:
+
+```
+https://example.test/page.php?PHP_DEBUGGER_TRIGGER=1
+```
 
-:::note
-This page is a work in progress — full documentation is coming soon.
 :::
+
+## Variables without a `PHP_DEBUGGER_` name
+
+Two more are read, both inherited and neither renamed:
+
+| Variable | |
+| --- | --- |
+| `DBGP_IDEKEY` | Supplies the session identifier when `php_debugger.idekey` is empty |
+| `DBGP_COOKIE` | Passed back to the client in the opening protocol message |
+
+Both exist so that a DBGp proxy can identify the session it set up. You are unlikely
+to set either by hand.
+
+## The `XDEBUG_` prefix
+
+Every variable above whose name begins `PHP_DEBUGGER_` also works with an `XDEBUG_`
+prefix — `XDEBUG_CONFIG`, `XDEBUG_IGNORE`, `XDEBUG_MODE`, `XDEBUG_SESSION`,
+`XDEBUG_SESSION_START` and `XDEBUG_TRIGGER`.
+
+The `XDEBUG_` spelling is checked first, so where both are set that one wins. The
+`PHP_DEBUGGER_` names are the ones to prefer in anything new.

docs/user-guide/starting-the-debugger.md

@@ -73,8 +73,8 @@ The debugger looks for a trigger under any of these names, in this order:
 3. `XDEBUG_SESSION`
 4. `PHP_DEBUGGER_SESSION`
 
-Each is looked for in the environment first, then `$_GET`, then `$_POST`, then
-`$_COOKIE`. So both of these start a session:
+Each is looked for in `$_GET`, then `$_POST`, then `$_COOKIE`, and last of all in
+the environment. So both of these start a session:
 
 ```bash
 PHP_DEBUGGER_TRIGGER=1 php your-script.php

docusaurus.config.js

@@ -123,7 +123,7 @@ const config = {
             position: 'left',
           },
           {
-            to: '/reference/cli-options',
+            to: '/reference/settings',
             label: 'Reference',
             position: 'left',
           },

sidebars.js

@@ -49,7 +49,6 @@ const sidebars = {
       items: [
         'reference/settings',
         'reference/functions',
-        'reference/cli-options',
         'reference/environment-variables',
         'reference/debug-protocol',
       ],