diff --git a/src/errors/opt_err.rs b/src/errors/opt_err.rs
index 40d7821..8172678 100644
--- a/src/errors/opt_err.rs
+++ b/src/errors/opt_err.rs
@@ -90,7 +90,7 @@ pub enum InvalidOption {
         /// The store key of the option configuration that caused this error.
         store_key: String,
 
-        /// The option name that caused this error.
+        /// The duplicated name of the option configuration.
         name: String,
     },
 
diff --git a/src/lib.rs b/src/lib.rs
index 1c0240c..484c485 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -545,8 +545,8 @@ impl<'b, 'a> Cmd<'a> {
     /// Returns the option argument with the specified name.
     ///
     /// If the option has multiple arguments, this method returns the first argument.
-    /// If the option a boolean flag, this method returns [None].
-    /// If the option is not specified in the command line argument, the return value
+    /// If the option is a boolean flag, this method returns [None].
+    /// If the option is not specified in the command line arguments, the return value
     /// of this method is [None].
     pub fn opt_arg(&'a self, name: &str) -> Option<&'a str> {
         if let Some(opt_vec) = self.opts.get(name) {
@@ -560,8 +560,8 @@ impl<'b, 'a> Cmd<'a> {
     /// Returns the option arguments with the specified name.
     ///
     /// If the option has one or multiple arguments, this method returns an array of the arguments.
-    /// If the option a boolean flag, this method returns an empty vector.
-    /// If the option is not specified in the command line argument, the return value
+    /// If the option is a boolean flag, this method returns an empty vector.
+    /// If the option is not specified in the command line arguments, the return value
     /// of this method is [None].
     pub fn opt_args(&'a self, name: &str) -> Option<&'a [&'a str]> {
         match self.opts.get(name) {
diff --git a/src/parse/parse_with.rs b/src/parse/parse_with.rs
index 51799a1..ba9a34e 100644
--- a/src/parse/parse_with.rs
+++ b/src/parse/parse_with.rs
@@ -21,9 +21,21 @@ impl<'b, 'a> Cmd<'a> {
     /// An option configuration has fields: `store_key`, `names`, `has_arg`, `is_array`,
     /// `defaults`, `desc`, `arg_in_help`, and `validator`.
     ///
+    /// When an option matches one of the `names` in the option configurations, the option is
+    /// registered into [Cmd] with `store_key`.
+    /// If both `has_arg` and `is_array` is false, the optioin can have only one option argument,
+    /// otherwise the option cannot have option arguments.
+    /// If `defaults` field is specified and no option value is given in command line arguments,
+    /// the value of `defaults` is set as the option arguments.
+    ///
+    /// If options not declared in option configurations are given in command line arguments, this
+    /// method basicaly returns [UnconfiguredOption] error.
+    /// However, if you want to allow other ooptions, add an option configuration of which
+    /// `store_key` or the first element of `names` is "*".
+    ///
     /// The ownership of the vector of option configurations which is passed as an argument of
-    /// this method is moved to this method and set to the public field `cfgs` of [Cmd] instance.
-    /// If you want to access the option configurations after parsing, get them from this field.
+    /// this method is moved to this method and set into this [Cmd] instance.
+    /// It can be retrieved with its method: [Cmd::opt_cfgs].
     ///
     /// ```
     /// use cliargs::{Cmd, OptCfg};
@@ -74,6 +86,10 @@ impl<'b, 'a> Cmd<'a> {
     /// This method parses command line arguments in the same way as the [Cmd::parse_with] method,
     /// except that it only parses the command line arguments before the first command argument.
     ///
+    /// The ownership of the vector of option configurations which is passed as an argument of
+    /// this method is moved to this method and set into this [Cmd] instance.
+    /// It can be retrieved with its method: [Cmd::opt_cfgs].
+    ///
     /// ```
     /// use cliargs::{Cmd, OptCfg};
     /// use cliargs::OptCfgParam::{names, has_arg, defaults, validator, desc, arg_in_help};