Add documentation on parsing life cycle and hooks

Readme.md

@@ -730,6 +730,8 @@ The supported events are:
 | `preAction`, `postAction` |  before/after action handler for this command and its nested subcommands |   `(thisCommand, actionCommand)` |
 | `preSubcommand` | before parsing direct subcommand  | `(thisCommand, subcommand)` |
 
+For an overview of the life cycle events see [parsing life cycle and hooks](./docs/parsing-and-hooks.md).
+
 ## Automated help
 
 The help information is auto-generated based on the information commander already knows about your program. The default
@@ -1114,6 +1116,7 @@ There is more information available about:
 
 - [deprecated](./docs/deprecated.md) features still supported for backwards compatibility
 - [options taking varying arguments](./docs/options-taking-varying-arguments.md)
+- [parsing life cycle and hooks](./docs/parsing-and-hooks.md)
 
 ## Support
 

docs/parsing-and-hooks.md

@@ -0,0 +1,23 @@
+# Parsing life cycle and hooks
+
+The processing starts with an array of args. Each command processes and removes the options it understands, and passes the remaining args to the next subcommand.
+The final command calls the action handler.
+
+Starting with top-level command (program):
+
+- parse options: parse recognised options (for this command) and remove from args
+- parse env: look for environment variables (for this command)
+- process implied: set any implied option values (for this command)
+- if the first arg is a subcommand
+    - call `preSubcommand` hooks
+    - pass remaining arguments to subcommand, and process same way
+
+Once reach final (leaf) command:
+
+- check for missing mandatory options
+- check for conflicting options
+- check for unknown options
+- process remaining args as command-arguments
+- call `preAction` hooks
+- call action handler
+- call `postAction` hooks