Revert "Revert "Revert "docs: Clarify corner caseses with default val…

…ues"""

This reverts commit 98f696c.

This was previously missed.  See clap-rs#3076

src/build/arg/mod.rs

@@ -612,6 +612,8 @@ impl<'help> Arg<'help> {
     ///
     /// **NOTE:** [Conflicting] rules and [override] rules take precedence over being required
     ///
+    /// **NOTE:** An argument is considered present when there is a [`Arg::default_value`]
+    ///
     /// # Examples
     ///
     /// ```rust
@@ -3728,6 +3730,8 @@ impl<'help> Arg<'help> {
     /// This argument is [required] only if the specified `arg` is present at runtime and its value
     /// equals `val`.
     ///
+    /// **NOTE:** An argument is considered present when there is a [`Arg::default_value`]
+    ///
     /// # Examples
     ///
     /// ```rust
@@ -3971,6 +3975,8 @@ impl<'help> Arg<'help> {
     /// if this arg (`self`) is present and its value equals to `val`.
     /// If it does, `another_arg` will be marked as required.
     ///
+    /// **NOTE:** An argument is considered present when there is a [`Arg::default_value`]
+    ///
     /// # Examples
     ///
     /// ```rust
@@ -4029,6 +4035,8 @@ impl<'help> Arg<'help> {
     ///
     /// The requirement will only become valid if this arg's value equals `val`.
     ///
+    /// **NOTE:** An argument is considered present when there is a [`Arg::default_value`]
+    ///
     /// # Examples
     ///
     /// ```rust
@@ -4082,6 +4090,8 @@ impl<'help> Arg<'help> {
     /// **NOTE:** [Conflicting] rules and [override] rules take precedence over being required
     /// by default.
     ///
+    /// **NOTE:** An argument is considered present when there is a [`Arg::default_value`]
+    ///
     /// # Examples
     ///
     /// ```rust
@@ -4155,6 +4165,8 @@ impl<'help> Arg<'help> {
     ///
     /// **NOTE** [`Arg::exclusive(true)`] allows specifying an argument which conflicts with every other argument.
     ///
+    /// **NOTE:** An argument is considered present when there is a [`Arg::default_value`]
+    ///
     /// # Examples
     ///
     /// ```rust
@@ -4203,6 +4215,8 @@ impl<'help> Arg<'help> {
     ///
     /// **NOTE:** [`Arg::exclusive(true)`] allows specifying an argument which conflicts with every other argument.
     ///
+    /// **NOTE:** An argument is considered present when there is a [`Arg::default_value`]
+    ///
     /// # Examples
     ///
     /// ```rust

src/build/arg_group.rs

@@ -240,6 +240,9 @@ impl<'help> ArgGroup<'help> {
     /// Use of more than one arg is an error." Vice setting `ArgGroup::multiple(true)` which
     /// states, '*At least* one arg from this group must be used. Using multiple is OK."
     ///
+    /// **NOTE:** An argument is considered present when there is a
+    /// [`Arg::default_value`](crate::Arg::default_value)
+    ///
     /// # Examples
     ///
     /// ```rust
@@ -274,6 +277,9 @@ impl<'help> ArgGroup<'help> {
     /// [argument requirement rules], you can name other arguments or groups that must be present
     /// when any one of the arguments from this group is used.
     ///
+    /// **NOTE:** An argument is considered present when there is a
+    /// [`Arg::default_value`](crate::Arg::default_value)
+    ///
     /// **NOTE:** The name provided may be an argument or group name
     ///
     /// # Examples
@@ -312,6 +318,9 @@ impl<'help> ArgGroup<'help> {
     ///
     /// **NOTE:** The names provided may be an argument or group name
     ///
+    /// **NOTE:** An argument is considered present when there is a
+    /// [`Arg::default_value`](crate::Arg::default_value)
+    ///
     /// # Examples
     ///
     /// ```rust
@@ -352,6 +361,9 @@ impl<'help> ArgGroup<'help> {
     ///
     /// **NOTE:** The name provided may be an argument, or group name
     ///
+    /// **NOTE:** An argument is considered present when there is a
+    /// [`Arg::default_value`](crate::Arg::default_value)
+    ///
     /// # Examples
     ///
     /// ```rust
@@ -385,6 +397,9 @@ impl<'help> ArgGroup<'help> {
     ///
     /// **NOTE:** The names provided may be an argument, or group name
     ///
+    /// **NOTE:** An argument is considered present when there is a
+    /// [`Arg::default_value`](crate::Arg::default_value)
+    ///
     /// # Examples
     ///
     /// ```rust