Complicated regex in ValidatePattern breaks the grammar

``` powershell
Function Get-Domain
{
    [CmdletBinding()]
    param(
        [ValidatePattern('^(?=^.{1,254}$)(^(?:(?!\d+\.)[a-zA-Z0-9_\-]{1,63}\.?)+(?:[a-zA-Z]{2,})$)')]
        [Parameter(ValueFromPipeline = $true)] # this line should not be highlighted as a string
        [string]$domain
    )
}
```
