关于变量属性？

请问下面这些语句中的[ ]里的内容都是什么意思呢？是属于那方面的知识点呢？想找资料都无从下手了。Thx：（

$ticket.Fields["Microsoft.Azure.Incident.Severity"].Value


Show-PopUp{
    [CmdletBinding()][OutputType([int])]Param(
        [parameter(Mandatory=$true, ValueFromPipeLine=$true)][Alias("Msg")][string]$Message,
        [parameter(Mandatory=$false, ValueFromPipeLine=$false)][Alias("Ttl")][string]$Title = $null,
        [parameter(Mandatory=$false, ValueFromPipeLine=$false)][Alias("Duration")][int]$TimeOut = 0,
        [parameter(Mandatory=$false, ValueFromPipeLine=$false)][Alias("But","BS")][ValidateSet( "OK", "OC", "AIR", "YNC" , "YN" , "RC")][string]$ButtonSet = "OK",
        [parameter(Mandatory=$false, ValueFromPipeLine=$false)][Alias("ICO")][ValidateSet( "None", "Critical", "Question", "Exclamation" , "Information" )][string]$IconType = "None"
         )

···
}