CmdletBinding - makes a function work like a compiled cmdlet.

CmdletBinding.ps1

# The CmdletBinding attribute is an attribute of functions that makes them operate 
# like compiled cmdlets that are written in C#, and it provides access to features of cmdlets.
# https://docs.microsoft.com/en-us/powershell/module/microsoft.powershell.core/about/about_functions_cmdletbindingattribute?view=powershell-6

[CmdletBinding()]
param(
  # Input params
  [string]${inputParam},

  # Example with validator and help message
  [Parameter(HelpMessage="Output directory")]
  [ValidateScript({$_ -notmatch "\.exe$"})]
  [string]${outputDir} = 'out',

  # Environment Variable usage
  [string] $param = $env:PARAM,

  # Switch param
  [switch] $someFlag
)