docs: Add a few code lang labels, minor cleanup

src/docs/markdown/caddyfile/concepts.md

@@ -141,13 +141,13 @@ directive "\"abc def\""
 
 Inside quoted tokens, all other characters are treated literally, including spaces, tabs, and newlines.
 
-You can also use a backtick (`\``) to quote tokens:
+You can also use a backtick <code>`</code> to quote tokens:
 
-```
+```caddy-d
 directive `"foo bar"`
 ```
 
-Backtick strings are convenient when tokens contain quote literals.
+Backtick strings are convenient when tokens contain quote literals, e.g. JSON text.
 
 
 
@@ -231,6 +231,7 @@ You can use any [Caddy placeholders](/docs/conventions#placeholders) in the Cadd
 | `{host}`        | `{http.request.host}`           |
 | `{labels.*}`    | `{http.request.host.labels.*}`  |
 | `{hostport}`    | `{http.request.hostport}`       |
+| `{port}`        | `{http.request.port}`           |
 | `{method}`      | `{http.request.method}`         |
 | `{path}`        | `{http.request.uri.path}`       |
 | `{path.*}`      | `{http.request.uri.path.*}`     |

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

@@ -142,7 +142,7 @@ transport http {
 - **tls_insecure_skip_verify** turns off security. _Do not use in production._
 - **tls_timeout** is a [duration value](/docs/conventions#durations) that specifies how long to wait for the TLS handshake to complete.
 - **tls_trusted_ca_certs** is a list of PEM files that specify CA public keys to trust when connecting to the backend.
-- **tls_server_name** sets the ServerName (SNI) to put in the ClientHello; only needed if the remote server it.
+- **tls_server_name** sets the ServerName (SNI) to put in the ClientHello; only needed if the remote server requires it.
 - **keepalive** is either `off` or a [duration value](/docs/conventions#durations) that specifies how long to keep connections open.
 - **keepalive_idle_conns** defines the maximum number of connections to keep alive.
 

src/docs/markdown/caddyfile/matchers.md

@@ -110,7 +110,7 @@ Defining a matcher with a unique name gives you more flexibility, allowing you t
 
 or, if there is only one matcher in the set:
 
-```
+```caddy-d
 @name ...
 ```
 
@@ -130,7 +130,7 @@ This proxies only the requests that have a header field named "Connection" conta
 
 If the matcher set consists of only one matcher, a one-liner syntax also works:
 
-```
+```caddy-d
 @post method POST
 reverse_proxy @post localhost:6001
 ```