Added basic selection docs.

docs/selection.md

@@ -0,0 +1,92 @@
+# Selection
+
+Two selection modes are supported:
+
+- Row selection allows the user to select whole rows
+- Cell selection allows the user to select individial cells
+
+Both selection types support either single or multiple selection. The default selection type is single row selection.
+
+## Index Paths
+
+Because `TreeDataGrid` supports hierarchical data, using a simple index to identify a row in the data source isn't enough. Instead indexes are represented using the `IndexPath` struct.
+
+An `IndexPath` is essentially an array of indexes, each element of which specifies the index at a succesively deeper level in the hierarchy of the data.
+
+Consider the following data source:
+
+```
+|- A
+|  |- B
+|  |- C
+|     |- D
+|- E
+```
+
+- `A` has an index path of `0` as it's the first item at the root of the hierarchy
+- `B` has an index path of `0,0` as it's the first child of the first item
+- `C` has an index path of `0,1` as it's the second child of the first item
+- `D` has an index path of `0,1,0` as it's the first child of `C`
+- `E` has an index path of `1` as it's the second item in the root
+
+`IndexPath` is an immutable struct which is constructed with an array of integers, e.g.: `new ItemPath(0, 1, 0)`. There is also an implicit conversion from `int` for when working with a flat data source.
+
+## Row Selection
+
+Row selection is the default and is exposed via the `RowSelection` property on the `FlatTreeDataGridSource<TModel>` and `HierarchicalTreeDataGridSource<TModel>` classes when enabled. Row selection is stored in an instance of the `TreeDataGridRowSelectionModel<TModel>` class.
+
+By default is single selection. To enable multiple selection set the the `SingleSelect` property to `false`, e.g.:
+
+```csharp
+Source = new FlatTreeDataGridSource<Person>(_people)
+{
+    Columns =
+    {
+        new TextColumn<Person, string>("First Name", x => x.FirstName),
+        new TextColumn<Person, string>("Last Name", x => x.LastName),
+        new TextColumn<Person, int>("Age", x => x.Age),
+    },
+};
+
+Source.RowSelection!.SingleSelect = false;
+```
+
+The properties on `ITreeDataGridRowSelectionModel<TModel>` can be used to manipulate the selection, e.g.:
+
+```csharp
+Source.RowSelection!.SelectedIndex = 1;
+```
+
+Or
+
+```csharp
+Source.RowSelection!.SelectedIndex = new IndexPath(0, 1);
+```
+
+## Cell Selection
+
+To enable cell selection for a `TreeDataGridSource`, assign an instance of `TreeDataGridCellSelectionModel<TModel>` to the source's `Selection` property:
+
+```csharp
+Source = new FlatTreeDataGridSource<Person>(_people)
+{
+    Columns =
+    {
+        new TextColumn<Person, string>("First Name", x => x.FirstName),
+        new TextColumn<Person, string>("Last Name", x => x.LastName),
+        new TextColumn<Person, int>("Age", x => x.Age),
+    },
+};
+
+Source.Selection = new TreeDataGridCellSelectionModel<Person>(Source);
+```
+
+Or for multiple cell selection:
+
+```csharp
+Source.Selection = new TreeDataGridCellSelectionModel<Person>(Source) { SingleSelect = false };
+```
+
+Cell selection is is exposed via the `CellSelection` property on the `FlatTreeDataGridSource<TModel>` and `HierarchicalTreeDataGridSource<TModel>` classes when enabled.
+
+The `CellIndex` struct indentifies an individual cell with by combination of an integer column index and an `IndexPath` row index.

readme.md

@@ -32,3 +32,4 @@ We accept issues and pull requests but we answer and review only pull requests a
 - [Creating a flat `TreeDataGrid`](docs/get-started-flat.md)
 - [Creating a hierarchical `TreeDataGrid`](docs/get-started-hierarchical.md)
 - [Supported column types](docs/column-types.md)
+- [Selection](docs/selection.md)