add missing API docs

Author: eiriktsarpalis

.gitignore

@@ -240,3 +240,6 @@ samples/framework/docker/MVCRandomAnswerGenerator/containerImage
 .DS_Store
 _dependentPackages/
 !/xml/System.Net.Cache/
+
+# Ignore ionide caches
+.ionide/

xml/System.Collections.Immutable/ImmutableArray`1+Builder.xml

@@ -439,7 +439,7 @@
         <Parameter Name="items" Type="System.ReadOnlySpan&lt;TDerived&gt;" Index="0" FrameworkAlternate="net-7.0" />
       </Parameters>
       <Docs>
-        <typeparam name="TDerived">To be added.</typeparam>
+        <typeparam name="TDerived">The type that derives from the type of item already in the array.</typeparam>
         <param name="items">The items to add at the end of the array.</param>
         <summary>Adds the specified items to the end of the array.</summary>
         <remarks>To be added.</remarks>

xml/System.Collections.Immutable/ImmutableArray`1.xml

@@ -351,7 +351,7 @@
         <Parameter Name="items" Type="System.Collections.Immutable.ImmutableArray&lt;TDerived&gt;" Index="0" FrameworkAlternate="net-7.0" />
       </Parameters>
       <Docs>
-        <typeparam name="TDerived">To be added.</typeparam>
+        <typeparam name="TDerived">The type that derives from the type of item already in the array.</typeparam>
         <param name="items">The values to add.</param>
         <summary>Adds the specified items to the end of the array.</summary>
         <returns>A new list with the elements added.</returns>
@@ -384,7 +384,7 @@
         <Parameter Name="items" Type="TDerived[]" Index="0" FrameworkAlternate="net-7.0" />
       </Parameters>
       <Docs>
-        <typeparam name="TDerived">To be added.</typeparam>
+        <typeparam name="TDerived">The type that derives from the type of item already in the array.</typeparam>
         <param name="items">The values to add.</param>
         <summary>Adds the specified items to the end of the array.</summary>
         <returns>A new list with the elements added.</returns>

xml/System.Collections.Immutable/ImmutableHashSet`1+Enumerator.xml

@@ -209,7 +209,7 @@
       </ReturnValue>
       <Docs>
         <summary>Gets the current element.</summary>
-        <value>To be added.</value>
+        <value>The element in the collection at the current position of the enumerator.</value>
         <remarks>
           <format type="text/markdown"><![CDATA[
 

xml/System.Collections.Immutable/ImmutableHashSet`1.xml

@@ -888,7 +888,8 @@
       </ReturnValue>
       <Docs>
         <summary>See the <see cref="T:System.Collections.Generic.ICollection`1" /> interface.</summary>
-        <value>To be added.</value>
+        <value>
+          <see langword="true" /> if the <see cref="T:System.Collections.Generic.ICollection`1" /> is read-only; otherwise, <see langword="false" />.</value>
         <remarks>To be added.</remarks>
       </Docs>
     </Member>
@@ -1275,7 +1276,8 @@
       </ReturnValue>
       <Docs>
         <summary>See the <see cref="T:System.Collections.ICollection" /> interface.</summary>
-        <value>To be added.</value>
+        <value>
+          <see langword="true" /> if access to the <see cref="T:System.Collections.ICollection" /> is synchronized (thread safe); otherwise, <see langword="false" />.</value>
         <remarks>
           <format type="text/markdown"><![CDATA[
 
@@ -1322,7 +1324,7 @@ This member is an explicit interface member implementation. It can be used only
       </ReturnValue>
       <Docs>
         <summary>See <see cref="T:System.Collections.ICollection" />.</summary>
-        <value>To be added.</value>
+        <value>An object that can be used to synchronize access to the <see cref="T:System.Collections.ICollection" />.</value>
         <remarks>
           <format type="text/markdown"><![CDATA[
 

xml/System.Collections.Immutable/ImmutableList`1+Builder.xml

@@ -1562,7 +1562,7 @@
         <param name="equalityComparer">The equality comparer to use in the search.
             If <see langword="null" />, <see cref="P:System.Collections.Generic.EqualityComparer`1.Default" /> is used.</param>
         <summary>Removes the first occurrence matching the specified value from this list.</summary>
-        <returns>To be added.</returns>
+        <returns>A value indicating whether the specified element was found and removed from the collection.</returns>
         <remarks>To be added.</remarks>
       </Docs>
     </Member>

xml/System.Collections.Immutable/ImmutableList`1+Enumerator.xml

@@ -223,7 +223,7 @@
       </ReturnValue>
       <Docs>
         <summary>The current element.</summary>
-        <value>To be added.</value>
+        <value>The element in the collection at the current position of the enumerator.</value>
         <remarks>
           <format type="text/markdown"><![CDATA[
 

xml/System.Collections.Immutable/ImmutableSortedDictionary`2+Enumerator.xml

@@ -223,7 +223,7 @@
       </ReturnValue>
       <Docs>
         <summary>The current element.</summary>
-        <value>To be added.</value>
+        <value>The element in the collection at the current position of the enumerator.</value>
         <remarks>
           <format type="text/markdown"><![CDATA[
 

xml/System.Collections.Immutable/ImmutableSortedSet`1+Enumerator.xml

@@ -231,7 +231,7 @@
       </ReturnValue>
       <Docs>
         <summary>The current element.</summary>
-        <value>To be added.</value>
+        <value>The element in the collection at the current position of the enumerator.</value>
         <remarks>
           <format type="text/markdown"><![CDATA[