Powershell v2 v3 Function Validate Schema

This function stems from more work on my PowerShell and XML book. I had pieced together a large portion of this function from the following Microsoft knowledge base article,

How To Validate an XML Document by Using DTD, XDR, or XSD in Visual C# .NET

As I worked further on it I ran into problems with the delegate so I read through some of Oisins posts on the topic, particularly this one:

PowerShell 2.0 RC: Working with .NET Callbacks – Part 1 - Synchronous  

Still unable to figure it out I posted on the PowerShell.org forums under the Advanced Scripting section,

Looking for the PowerShell way to write/add delegates

After some back and forth with Kirk, he finally got me in the ballpark and helped me find one of the few uses of Write-Host (delegates suppress Write-Output, so, you have to use another pipeline to get output from a delegate back to the host).  Once I had a working script, I converted it into the following function:

function Validate-Schema

{

      <#

            .EXAMPLE 1

                  Validate-Schema -XmlFilePath C:PowerShell and XMLproduct.xml -SchemaType DTD

                 

                  This example illustrates how to validate a DTD schema referenced directly from within the .xml file itself. This example includes an intentional error and outputs the following:

                 

                  Error: The required attribute ProductID is missing.

                  Document is invalid

                       

            .PARAMETER XmlFilePath

                  A mandatory parameter indicating the path to the .xml file.

                 

            .PARAMETER SchemaType

                  A mandatory parameter indicating whether the validation type is DTD or XSD. Default is XSD.

                 

            .OUTPUTS

                  Boolean.

                 

                  If you add the -Verbose switch the function will add comments indicating more specifically the item throwing the error during validation.

           

            .NOTES

                  Author: Will Steele (will.steele@live.com)

                  Date last modified: 2012/08/20

                  By default this script will validate against XSD and will only return a boolean value. If you want more verbose output add the -Verbose switch to the function when its called.

                 

      #>

                 

      [CmdletBinding()]

      param(

            [Parameter(

                  Mandatory = $true,

                  Position = 0

            )]

            [ValidateNotNullOrEmpty()]

            $XmlFilePath,

           

            [Parameter(

                  Mandatory = $true,

                  Position = 1

            )]

            [ValidateNotNullOrEmpty()]

            [ValidateSet(DTD,XSD)]

            $SchemaType = XSD

      )

     

      # Create delegate for handling/reporting errors

      [System.Xml.Schema.ValidationEventHandler] $onValidationError = {

            param(

                  $sender,

                  $eventArgs

            )

           

            $isValid = $false;

            Write-Verbose "Error: $($eventArgs.Message)";

      }

      # Set while loop flag

      $isValid = $true;

      # Instantiate XML text reader

      $XmlTextReader = New-Object -TypeName System.Xml.XmlTextReader($XmlFilePath)

     

      # Instantiate ValidatingReader and set ValidationType

      $XmlValidatingReader = New-Object -TypeName System.Xml.XmlValidatingReader($XmlTextReader)

      switch($SchemaType)

      {

            DTD

            {

                  $XmlValidatingReader.ValidationType = [System.Xml.ValidationType]::DTD;

            }

            XSD

            {

                  $XmlValidatingReader.ValidationType = [System.Xml.ValidationType]::Schema;

            }

      }

     

      # Add handler to Validating Reader

      $XmlValidatingReader.add_ValidationEventHandler($onValidationError)

     

      # Validate file

      while($XmlValidatingReader.Read()) {}

     

      # Close handles

      $XmlValidatingReader.Close()

      $XmlTextReader.Close()

      # Output whether the document is valid or invalid.

      if ($isValid)

      {

         Write-Verbose "Document is valid";

         $isValid

      }

      else

      {

         Write-Verbose "Document is invalid";

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