update doc book and readme with fixes

README.md

@@ -714,7 +714,7 @@ sub.subcommand = true
 Spaces before and after the name and argument are ignored. Multiple arguments are separated by spaces. One set of quotes will be removed, preserving spaces (the same way the command line works). Boolean options can be `true`, `on`, `1`, `yes`, `enable`; or `false`, `off`, `0`, `no`, `disable` (case insensitive). Sections (and `.` separated names) are treated as subcommands (note: this does not necessarily mean that subcommand was passed, it just sets the "defaults"). You cannot set positional-only arguments.  🆕 Subcommands can be triggered from configuration files if the `configurable` flag was set on the subcommand.  Then the use of `[subcommand]` notation will trigger a subcommand and cause it to act as if it were on the command line.
 
 To print a configuration file from the passed
-arguments, use `.config_to_str(default_also=false, prefix="", write_description=false)`, where `default_also` will also show any defaulted arguments, `prefix` will add a prefix, and `write_description` will include option descriptions.  See [Config files](https://cliutils.github.io/CLI11/book/chapters/config.html) for some additional details.
+arguments, use `.config_to_str(default_also=false, write_description=false)`, where `default_also` will also show any defaulted arguments, and `write_description` will include the app and option descriptions.  See [Config files](https://cliutils.github.io/CLI11/book/chapters/config.html) for some additional details.
 
 ### Inheriting defaults
 

book/chapters/config.md

@@ -80,7 +80,27 @@ The main differences are in vector notation and comment character.  Note: CLI11
 
 ## Writing out a configure file
 
-To print a configuration file from the passed arguments, use `.config_to_str(default_also=false, prefix="", write_description=false)`, where `default_also` will also show any defaulted arguments, `prefix` will add a prefix, and `write_description` will include option descriptions.
+To print a configuration file from the passed arguments, use `.config_to_str(default_also=false, write_description=false)`, where `default_also` will also show any defaulted arguments, and `write_description` will include option descriptions and the App description
+
+```cpp
+
+ CLI::App app;
+ app.add_option(...);
+    // several other options
+ CLI11_PARSE(app, argc, argv);
+ //the config printout should be after the parse to capture the given arguments
+ std::cout<<app.config_to_str(true,true);
+```
+
+if a prefix is needed to print before the options, for example to print a config for just a subcommand, the config formatter can be obtained directly.
+
+```cpp
+
+  auto fmtr=app.get_config_formatter();
+  //std::string to_config(const App *app, bool default_also, bool write_description, std::string prefix)
+  fmtr->to_config(&app,true,true,"sub.");
+  //prefix can be used to set a prefix before each argument,  like "sub."
+```
 
 ### Customization of configure file output
 The default config parser/generator has some customization points that allow variations on the TOML format.  The default formatter has a base configuration that matches the TOML format.  It defines 5 characters that define how different aspects of the configuration are handled
@@ -115,7 +135,7 @@ The default configuration file will read INI files, but will write out files in
 ```cpp
 app.config_formatter(std::make_shared<CLI::ConfigINI>());
 ```
-which makes use of a predefined modification of the ConfigBase class which TOML also uses.
+which makes use of a predefined modification of the ConfigBase class which TOML also uses. If a custom formatter is used that is not inheriting from the from ConfigBase class `get_config_formatter_base() will return a nullptr, so some care must be exercised in its us with custom configurations.  
 
 ## Custom formats
 

include/CLI/App.hpp

@@ -1491,7 +1491,7 @@ class App {
         return this;
     }
     /// Produce a string that could be read in as a config of the current values of the App. Set default_also to
-    /// include default arguments. Prefix will add a string to the beginning of each option.
+    /// include default arguments. write_descriptions will print a description for the App and for each option.  
     std::string config_to_str(bool default_also = false, bool write_description = false) const {
         return config_formatter_->to_config(this, default_also, write_description, "");
     }