Trying to figure out AllowedValues parameter metadata

pqDocumentationAllowedValues.md

let
  Source = 
    let
      func =  // fnPowerTrim              
      
        let
          input = (text as text, optional char_to_trim as text) =>
            let
              char = if char_to_trim = null then " " else char_to_trim, 
              split = Text.Split(text, char), 
              removeblanks = List.Select(split, each _ <> ""), 
              result = Text.Combine(removeblanks, char), 
              fnType = type function (
                optional char_to_trim as (
                  type text meta [Documentation.AllowedValues = {"-", ";", ":"}]
                )
              ) as list
                meta [
                  Documentation.Name            = "fnPowerTrim", 
                  Documentation.LongDescription = "Choose character to trim"
                ]
            in
              Value.ReplaceType(result, fnType)
        in
          input, 
      documentation = [
        Documentation.Name = " Function.PowerTrim ", 
        Documentation.Description = " Trims Excess Spaces. ", 
        Documentation.LongDescription
          = " Add Column, Invoke Custom Function, Choose Column to Trim. ", 
        Documentation.Category = " Trim Function ", 
        Documentation.Source = "  TVCA PowerBI Team  ", 
        Documentation.Version = " 02 / 09 / 2022 ", 
        Documentation.Author = " Imran Haq ", 
        Documentation.Examples = {
          [
            Description = "  Neat function to remove excess spaces   ", 
            Code        = " Trims   All   Spaces   ", 
            Result      = " Trims All Spaces "
          ]
        }
      ]
    in
      Value.ReplaceType(func, Value.ReplaceMetadata(Value.Type(func), documentation))
in
  Source