XML documentation for FastTree regression trainer. (#3412)

* XML documentation for FastTree regression trainer.

* PR feedback.

Author: codemzs

src/Microsoft.ML.FastTree/FastTreeArguments.cs

@@ -111,7 +111,8 @@ public Options()
     public sealed partial class FastTreeRegressionTrainer
     {
         /// <summary>
-        /// Options for the <see cref="FastTreeRegressionTrainer"/>.
+        /// Options for the <see cref="FastTreeRegressionTrainer"/> as used in
+        /// [FastTree(Options)](xref:Microsoft.ML.TreeExtensions.FastTree(Microsoft.ML.RegressionCatalog.RegressionTrainers,Microsoft.ML.Trainers.FastTree.FastTreeRegressionTrainer.Options)).
         /// </summary>
         [TlcModule.Component(Name = LoadNameValue, FriendlyName = UserNameValue, Desc = Summary)]
         public sealed class Options : BoostedTreeOptions, IFastTreeTrainerFactory

src/Microsoft.ML.FastTree/FastTreeRegression.cs

@@ -32,7 +32,28 @@ namespace Microsoft.ML.Trainers.FastTree
     /// <summary>
     /// The <see cref="IEstimator{TTransformer}"/> for training a decision tree regression model using FastTree.
     /// </summary>
-    /// <include file='doc.xml' path='doc/members/member[@name="FastTree_remarks"]/*' />
+    /// <remarks>
+    /// <format type="text/markdown"><![CDATA[
+    /// To create this trainer, use [FastTree](xref:Microsoft.ML.TreeExtensions.FastTree(Microsoft.ML.RegressionCatalog.RegressionTrainers,System.String,System.String,System.String,System.Int32,System.Int32,System.Int32,System.Double))
+    /// or [FastTree(Options)](xref:Microsoft.ML.TreeExtensions.FastTree(Microsoft.ML.RegressionCatalog.RegressionTrainers,Microsoft.ML.Trainers.FastTree.FastTreeRegressionTrainer.Options)).
+    ///
+    /// [!include[io](~/../docs/samples/docs/api-reference/io-columns-regression.md)]
+    ///
+    /// ### Trainer Characteristics
+    /// |  |  |
+    /// | -- | -- |
+    /// | Machine learning task | Regression |
+    /// | Is normalization required? | No |
+    /// | Is caching required? | No |
+    /// | Required NuGet in addition to Microsoft.ML | Microsoft.ML.FastTree |
+    ///
+    /// [!include[algorithm](~/../docs/samples/docs/api-reference/algo-details-fasttree.md)]
+    /// ]]>
+    /// </format>
+    /// </remarks>
+    /// <seealso cref="Microsoft.ML.TreeExtensions.FastTree(Microsoft.ML.RegressionCatalog.RegressionTrainers,System.String,System.String,System.String,System.Int32,System.Int32,System.Int32,System.Double)"/>
+    /// <seealso cref="Microsoft.ML.TreeExtensions.FastTree(Microsoft.ML.RegressionCatalog.RegressionTrainers,Microsoft.ML.Trainers.FastTree.FastTreeRegressionTrainer.Options)"/>
+    /// <seealso cref="Options"/>
     public sealed partial class FastTreeRegressionTrainer
         : BoostingFastTreeTrainerBase<FastTreeRegressionTrainer.Options, RegressionPredictionTransformer<FastTreeRegressionModelParameters>, FastTreeRegressionModelParameters>
     {

src/Microsoft.ML.FastTree/TreeTrainersCatalog.cs

@@ -14,11 +14,11 @@ namespace Microsoft.ML
     public static class TreeExtensions
     {
         /// <summary>
-        /// Predict a target using a decision tree regression model trained with the <see cref="FastTreeRegressionTrainer"/>.
+        /// Create <see cref="FastTreeRegressionTrainer"/>, which predicts a target using a decision tree regression model.
         /// </summary>
         /// <param name="catalog">The <see cref="RegressionCatalog"/>.</param>
-        /// <param name="labelColumnName">The name of the label column.</param>
-        /// <param name="featureColumnName">The name of the feature column.</param>
+        /// <param name="labelColumnName">The name of the label column. The column data must be <see cref="System.Single"/>.</param>
+        /// <param name="featureColumnName">The name of the feature column. The column data must be a known-sized vector of <see cref="System.Single"/>.</param>
         /// <param name="exampleWeightColumnName">The name of the example weight column (optional).</param>
         /// <param name="numberOfTrees">Total number of decision trees to create in the ensemble.</param>
         /// <param name="numberOfLeaves">The maximum number of leaves per decision tree.</param>
@@ -46,7 +46,7 @@ public static FastTreeRegressionTrainer FastTree(this RegressionCatalog.Regressi
         }
 
         /// <summary>
-        /// Predict a target using a decision tree regression model trained with the <see cref="FastTreeRegressionTrainer"/>.
+        /// Create <see cref="FastTreeRegressionTrainer"/> with advanced options, which predicts a target using a decision tree regression model.
         /// </summary>
         /// <param name="catalog">The <see cref="RegressionCatalog"/>.</param>
         /// <param name="options">Trainer options.</param>