This function shows a cleanly written and well documented function.

Test-IPv4Address.ps1

function Test-IPv4Address {
    [CmdletBinding()]
    param(
        [parameter(Mandatory=$true, ValueFromPipeline=$true, HelpMessage='Enter data to validate as IP Address.')]
        [alias('IPAddress')]
        [string]$IP
    )

    begin{}
    process{
        Write-Verbose -Message 'Checking to see if data entered is an IP address.'
        if ($IP -as [IPAddress])
        {
            Write-Verbose -Message 'Data has been validated as a valid IP addresss.'
            $true
        } else {
            Write-Verbose -Message 'Data has been validated as it is NOT a valid IP address.'
            $false
        }
        Write-Verbose -Message 'Finished validating data.'
    }
    end{}
    <#    
    .SYNOPSIS
        Validates an IP address.
    .DESCRIPTION
        This function takes data in and validates if it is an IP Address.
    .PARAMETER IP
        Data to be validated as an IP Address
    .INPUTS
        [System.String]
    .OUTPUTS
        [System.Bool]
    .EXAMPLE
        Test-IPv4Address -IP 10.0.0.1
          True
    .EXAMPLE
        Test-IPAddress -IP 260.150.3.1000
          False
    .LINK
        http://www.mwjcomputing.com
    .LINK
        http://github.com/mwjcomputing
    .NOTE
        This code was modified from a post at http://www.powershellmagazine.com/2014/07/23/how-ive-started-loving-powershell by Fabien Dibot.
    #>
}