diff --git a/Commands/Format.PS1XML/Write-FormatSelectionSet.ps1 b/Commands/Format.PS1XML/Write-FormatSelectionSet.ps1
new file mode 100644
index 0000000..dbffb23
--- /dev/null
+++ b/Commands/Format.PS1XML/Write-FormatSelectionSet.ps1
@@ -0,0 +1,83 @@
+function Write-FormatSelectionSet
+{
+    <#
+    .SYNOPSIS
+        Writes a selection set.
+    .DESCRIPTION
+        Writes a format selection set.
+    .NOTES    
+        Formatting is commonly selected by a TypeName.
+        
+        It can also be selected by a group of type names, which is called a SelectionSet.
+
+        A few built-in formatters use selection sets, most notably the filesystem formatters.
+    .EXAMPLE
+        Write-FormatSelectionSet -Name 'FileSystemTypes' -TypeName 'System.IO.DirectoryInfo', 'System.IO.FileInfo'    
+    #>
+    param(
+    # The name of the selection set.
+    [Parameter(Mandatory,ValueFromPipelineByPropertyName)]
+    [Alias('SelectionSetName','SelectionSet')]
+    [string]
+    $Name,
+
+    # The type names in the selection set.
+    [Parameter(Mandatory,ValueFromPipelineByPropertyName)]
+    [string[]]
+    $TypeName
+    )
+
+    begin {
+        # First, create a queue to hold the selection sets.
+        $eachSelectionSet = [Collections.Queue]::new()
+    }
+    
+    process {
+        # Make sure the name and type names are XML-safe
+        $NameAsXml = "<Name>$Name</Name>" -as [xml]
+        if (-not $NameAsXml) {
+            $Name = [Security.SecurityElement]::Escape($Name)
+        }
+        $TypeName = foreach ($tn in $TypeName) {
+            if (-not ("<TypeName>$tn</TypeName>" -as [xml])) {
+                [Security.SecurityElement]::Escape($tn)
+            } else {
+                $tn
+            }
+        }
+
+        # Create the selection set XML
+        $selectionSetXml = [xml](@(
+            "<SelectionSet>"
+                # Consisting of a `<Name>`
+                "<Name>$Name</Name>"                
+                "<Types>" # and a `<Types>` element
+                    foreach ($tn in $TypeName) {
+                        # (containing each `<TypeName>`)
+                        "<TypeName>$tn</TypeName>"
+                    }
+                "</Types>"
+            "</SelectionSet>"
+        ) -join '')
+        if (-not $selectionSetXml) { return }
+        $xOut=[IO.StringWriter]::new()
+        $selectionSetXml.Save($xOut)
+        $eachSelectionSet.Enqueue("$xOut" -replace '\<\?xml.+?\?>[\s\r\n]+')
+        $xOut.Dispose()
+    }
+
+    end {
+        # Create the `<SelectionSets>` element
+        $selectionSetXml = @(
+            "<SelectionSets>"
+            # (containing each `<SelectionSet>`)
+            $eachSelectionSet.ToArray()
+            "</SelectionSets>"
+        ) -join '' -as [xml]
+        $xOut=[IO.StringWriter]::new()
+        $selectionSetXml.Save($xOut)
+        # Write the XML to the pipeline as a string, removing the XML declaration.
+        "$xOut" -replace '\<\?xml.+?\?>[\s\r\n]+'
+        $xOut.Dispose()
+    }
+}