Q:

Accepting an optional parameter only as named, not positional

I'm writing a PowerShell script that's a wrapper to an .exe. I want to have some optional script params, and pass the rest directly to the exe. Here's a test script:
param (
    [Parameter(Mandatory=$False)] [string] $a = "DefaultA"
   ,[parameter(ValueFromRemainingArguments=$true)][string[]]$ExeParams   # must be string[] - otherwise .exe invocation will quote
)

Write-Output ("a=" + ($a) + "  ExeParams:") $ExeParams

If I run with the a named param, everything is great:
C:\ > powershell /command \temp\a.ps1 -a A This-should-go-to-exeparams This-also
a=A  ExeParams:
This-should-go-to-exeparams
This-also

However, if I try to omit my param, the first unnamed param is assigned to it:
C:\ > powershell /command \temp\a.ps1 This-should-go-to-exeparams This-also
a=This-should-go-to-exeparams  ExeParams:
This-also

I would expect:
a=DefaultA ExeParams:
This-should-go-to-exeparams
This-also

I tried adding Position=0 to the param, but that produces the same result.
Is there a way to achieve this?
Maybe a different parameter scheme?

A:

By default, all function parameters are positional. Windows PowerShell assigns position numbers to parameters in the order in which the parameters are declared in the function. To disable this feature, set the value of the PositionalBinding argument of the CmdletBinding attribute to $False.
have a look at How to disable positional parameter binding in PowerShell 
function Test-PositionalBinding
{
    [CmdletBinding(PositionalBinding=$false)]
    param(
       $param1,$param2
    )

    Write-Host param1 is: $param1
    Write-Host param2 is: $param2
}

