docs: Add handle_errors, CEL matcher; a few other improvements

src/docs/markdown/caddyfile/directives.md

@@ -13,6 +13,7 @@ Directive | Description
 **[encode](/docs/caddyfile/directives/encode)** | Encodes (usually compresses) responses
 **[file_server](/docs/caddyfile/directives/file_server)** | Serve files from disk
 **[handle](/docs/caddyfile/directives/handle)** | A mutually-exclusive group of directives
+**[handle_errors](/docs/caddyfile/directives/handle_errors)** | Defines routes for handling errors
 **[header](/docs/caddyfile/directives/header)** | Sets or removes response headers
 **[log](/docs/caddyfile/directives/log)** | Enables access/request logging
 **[php_fastcgi](/docs/caddyfile/directives/php_fastcgi)** | Serve PHP sites over FastCGI

src/docs/markdown/caddyfile/directives/file_server.md

@@ -13,7 +13,7 @@ A static file server. It works by appending the request's URI path to the [site'
 file_server [<matcher>] [browse] {
 	root   <path>
 	hide   <files...>
-	index  <files...>
+	index  <filenames...>
 	browse [<template_file>]
 }
 ```
@@ -21,6 +21,7 @@ file_server [<matcher>] [browse] {
 - **browse** enables file listings for requests to directories that do not have an index file.
 - **root** sets the path to the site root for just this file server instance, overriding any other. Default: `{http.vars.root}` or the current working directory. Note: When specified as a subdirective like this, only this directive will know this root; for other directives (like [try_files](/docs/caddyfile/directives/try_files) or [templates](/docs/caddyfile/directives/templates)) to know the same site root, use the [root](/docs/caddyfile/directives/root) directive, not subdirective.
 - **hide** is a list of files to hide; if requested, the file server will pretend they do not exist. The active configuration file will be added by default.
+- **index** is a list of filenames to look for as index files. Default: `index.html index.txt`
 - **<template_file>** is an optional custom template file to use for directory listings.
 
 

src/docs/markdown/caddyfile/directives/handle_errors.md

@@ -0,0 +1,19 @@
+---
+title: handle_errors (Caddyfile directive)
+---
+
+# handle_errors
+
+Sets up error handlers.
+
+When the normal HTTP request handlers return an error, normal procesing stops and the error handlers are invoked. Error handlers form a route which is just like normal routes, and they can do anything that normal routes can do. This enables great control and flexibility when handling errors during HTTP requests.
+
+## Syntax
+
+```
+handle_errors {
+	<directives...>
+}
+```
+
+- **<directives...>** is a list of HTTP handler directives, directive blocks, or matchers; one per line.

src/docs/markdown/caddyfile/matchers.md

@@ -121,6 +121,7 @@ For most matchers that accept multiple values, those values are OR'ed; i.e. one
 
 Full matcher documentation can be found [in each respective matcher module's docs](/docs/json/apps/http/servers/routes/match/).
 
+- [expression](#expression)
 - [file](#file)
 - [header](#header)
 - [header_regexp](#header-regexp)
@@ -134,6 +135,26 @@ Full matcher documentation can be found [in each respective matcher module's doc
 - [remote_ip](#remote-ip)
 
 
+
+### expression
+
+```
+expression <cel...>
+```
+
+By any [CEL (Common Expression Language)](https://github.com/google/cel-spec) expression that returns `true` or `false`.
+
+⚠️ This module is still experimental and, as such, may experience breaking changes.
+
+As a special case, Caddy [placeholders](/docs/conventions#placeholders) (or [Caddyfile shorthands](/docs/caddyfile/concepts#placeholders)) may be used in these CEL expressions, as they are preprocessed and converted to regular CEL function calls before being interpreted by the CEL environment.
+
+Examples:
+
+```
+expression {method}.startsWith("P")
+```
+
+
 ### file
 
 ```