A PowerShell script that formats the output of the Test-HtmlValidity script. Also support grouped input on the URL property.

Format-HtmlValidityOutput.ps1

<#
.SYNOPSIS
    Formats the output of the Test-HtmlValidity script
.DESCRIPTION
    Formats the output of the Test-HtmlValidity script. Also support grouped input on the URL property. 
.NOTES
    Author: Michaël Hompus
    License: This work is licensed under a Creative Commons Attribution-ShareAlike 2.5 Generic License.
.PARAMETER Messages
    One or more output messages from the HTML validity PowerShell Script.
.LINK
    Invoke-RestMethod
    https://gist.github.com/eNeRGy164/2bc35ceb31104d7a2d48d2993e92354b
    https://gist.github.com/eNeRGy164/ffb410e6dc6acb8610af3e4a1a85437c
.EXAMPLE
    Test-HtmlValidity.ps1 -Urls https://blog.hompus.nl/ | .\Format-HtmlValidityOutput.ps1
.EXAMPLE
    Test-HtmlValidity.ps1 -Urls https://blog.hompus.nl,https://blog.hompus.nl/about/ | .\Format-HtmlValidityOutput.ps1
.EXAMPLE
    Test-HtmlValidity.ps1 -Urls https://blog.hompus.nl,https://blog.hompus.nl/about/ | Group-Object Url | .\Format-HtmlValidityOutput.ps1
#>
[CmdletBinding()]
Param(
    [Parameter(Mandatory = $true, ValueFromPipeline = $true, ValueFromPipelineByPropertyName = $true)]
    [PSObject[]]
    $Messages
)

BEGIN {
    if ($null -eq $Messages) { 
        $Messages = @($input) 
    }
}

PROCESS {
    Function Write-FormattedMessages {
        [CmdletBinding()]
        param(
            [Switch]$IsGrouped = $false,
            [Switch]$HideUrl = $false
        )
    
        if (-not $IsGrouped -or -not $HideUrl) {
            Write-Host -ForegroundColor DarkCyan $_.Url
            Write-Host 
        }

        if ($_.Type -eq "error") {
            Write-Host -NoNewline -ForegroundColor Red "   Error "
        } elseif ($_.Type -eq "warning") {
            Write-Host -NoNewline -ForegroundColor Yellow " Warning "
        } elseif ($_.Type -eq "Valid") {
            Write-Host -NoNewline -ForegroundColor Green "   Valid "
        } else {
            Write-Host -NoNewline -ForegroundColor White "    Info "
        }

        if ($_.Type -ne "Valid") {
            Write-Host -NoNewline $_.Message
            Write-Host -ForegroundColor DarkGray " ($($_.LastLine), $($_.LastColumn))"

            $HiliteEnd = ($_.HiliteStart + $_.HiliteLength)

            Write-Host -NoNewline "         "

            for ($i = 0; $i -lt $_.HiliteStart; $i++) {
                Write-Host -NoNewline -BackgroundColor DarkBlue  $_.Extract[$i]
            }

            for ($i = $_.HiliteStart; $i -lt $HiliteEnd; $i++) {
                Write-Host -NoNewline -BackgroundColor Black -ForegroundColor Yellow $_.Extract[$i]
            }

            for ($i = $HiliteEnd; $i -lt $_.Extract.Length; $i++) {
                Write-Host -NoNewline -BackgroundColor DarkBlue $_.Extract[$i]
            }
        }

        Write-Host
        Write-Host
    }

    if ($Messages.Group -ne $null) {
        Write-Host -ForegroundColor DarkCyan $_.Name
        Write-Host
        
        $hideUrl = ($_.Name -eq $_.Group[0].url)

        $Messages.Group | ForEach-Object { Write-FormattedMessages -IsGrouped -HideUrl:$hideUrl }
    } else {
        $Messages | ForEach-Object { Write-FormattedMessages }
    }
}