Update readme.

Author: dpse

README.md

@@ -27,13 +27,12 @@ History and output buffering can be disabled to reduce memory requirements for u
 - Default commands (`help`, `clear`, `login`, and `logout`)
 
 Users can be registered so that only certain commands are available to certain users.
-Login is possibly with either password only or with usernames and optional passwords.
+Login is possible with either password only or with usernames and optional passwords.
 Only users with a level matching the minimum required level for a command can execute the command.
 
-Commands are registered with a command, the minimum user level required (if users are enabled),
-the minimum and maximum number of arguments that are allowed, and a description.
-The description is automatically printed when the command is invoked with "-h/--help" flags or when the built-in
-help command is called.
+Commands are registered with a command, the minimum user level required (if users are enabled), a description, and
+optionally a pattern with some options (if pattern matching is enabled).
+The description along with any pattern and options (if used) are automatically printed when the built-in help command is called.
 
 #### Pattern Matching
 
@@ -50,7 +49,8 @@ The following syntax can be used in patterns:
 | `a\|(b c)` or `a\|{b c}`                             | Matches `a` or `b c`.                         |
 | `...` | Matches none or all remaining tokens.          |
 
-The pattern matching system currently only supports matching word-tokens (i.e. no matches inside words).
+- The pattern matching system currently only supports matching word-tokens (i.e. no matches inside words).
+- The pattern matcher is recursive and stack requirements will increase with pattern complexity.
 
 ## Usage
 
@@ -61,7 +61,7 @@ The pattern matching system currently only supports matching word-tokens (i.e. n
 
 void output(void * arg, const char * str)
 {
-    printf("%s", str);
+    printf("%s", str); // Or send through serial interface
 }
 
 tclie_t tclie;
@@ -72,9 +72,9 @@ tclie_init(&tclie, output, NULL);
 
 ```c
 static const tclie_user_t users[] = {
-    // Name, password, level
-    {"debug", NULL, 1},
-    {"admin", "12345", 2}
+    // Name,  password, level
+    {"debug", NULL,     1}, // No password required
+    {"admin", "12345",  2}
 };
 
 tclie_reg_users(&tclie, users, 2);
@@ -92,7 +92,7 @@ int echo(void * arg, int argc, const char ** argv)
 }
 
 static const tclie_cmd_t cmds[] = {
-    // Name, callback, min user level, min args, max args, description (for help)    
+    // Name, callback, minimum user level, description (for help)    
     {"echo", echo, 1, "Echo input."}
 };
 
@@ -110,6 +110,17 @@ while (1) {
 
 See the examples directory for more details.
 
+### Logging
+
+In a multithreaded environment it can be useful to be able to log stuff without disturbing the prompt:
+
+```c
+tclie_log(&tclie, "Some message...\r\n");
+
+char buf[64];
+tclie_log_printf(&tclie, buf, sizeof(buf), "Hello %s\r\n", "world!");
+```
+
 ## Supported Keyboard Shortcuts
 
 | Shortcut | Description                                             |
@@ -136,5 +147,26 @@ See the examples directory for more details.
 | Alt+f    | Move cursor forward one word.                           |
 | Alt+r    | Cancel changes to history line.                         |
 | Tab      | Tab-complete at cursor or select from multiple matches. |
-| Esc        | Exit tab-completion or reverse search mode.                |
+| Esc      | Exit tab-completion or reverse search mode.             |
+
+*Note! `Esc` needs to be pressed twice since it is impossible to differentiate from an escape sequence otherwise.*
 
+## Miscellaneous
+
+### Telnet
+
+Telnet newlines (`<CR><NUL>`) are automatically handled but it may be necessary to tell connecting clients (e.g.
+PuTTY) how to behave.
+This can be done by sending the following sequences to the client:
+
+- `IAC DO ECHO`: Tell client to echo received characters from server.
+- `IAC WILL ECHO`: Tell client that the server will echo back received characters.
+- `IAC DO SUPPRESS-GO-AHEAD`: Tell client to not send `GO AHEAD` when transmitting.
+- `IAC WILL SUPPRESS-GO-AHEAD`: Tell client that the server won't send `GO AHEAD` when transmitting.
+
+```c
+const char options[] = {255, 253, 1,  // IAC DO ECHO
+                        255, 251, 1,  // IAC WILL ECHO
+                        255, 253, 3,  // IAC DO SUPPRESS-GO-AHEAD
+                        255, 251, 3}; // IAC WILL SUPPRESS-GO-AHEAD
+```