return $result
  }

  #
  # NOTE: This procedure returns the list of API keys to use when looking
  #       up packages via the package repository server.  An empty list
  #       is returned if no API keys are currently configured.  There are
  #       no arguments.
  #
  # <public>
  proc getLookupApiKeys {} {
    set varName [appendArgs [getLookupVarNamePrefix] api_keys]
  #       is returned if no API keys are currently configured.  The prefix
  #       argument is an extra variable name prefix to check prior to any
  #       that are already configured.
  #
  # <internal>
  proc getApiKeys { {prefix ""} } {
    global env

    set prefixes [list]

    if {[string length $prefix] > 0} then {
      lappend prefixes $prefix
    }

    lappend prefixes [getLookupVarNamePrefix]

    foreach prefix $prefixes {
      if {[string length $prefix] == 0} then {
        set prefix ::; # TODO: Make non-global?
      }

      set varName [appendArgs $prefix api_keys]

    if {[info exists $varName]} then {
      return [set $varName]
    }
      if {[info exists $varName]} then {
        return [set $varName]
      }

    global env
    set varName [string trim $varName :]
      set varName [string trim $varName :]

    if {[info exists env($varName)]} then {
      return $env($varName)
      if {[info exists env($varName)]} then {
        return $env($varName)
      }
    }

    return [list]; # NOTE: System default, which is "public-only".
  }

  #
  # NOTE: This procedure returns the base URI for the package repository

  #
  # <public>
  proc getPackageFromRepository { package version caller } {
    #
    # NOTE: Get the list of API keys and try each one, in order, until
    #       the package is found.
    #
    set apiKeys [getLookupApiKeys]; lappend apiKeys ""
    set apiKeys [getApiKeys]; lappend apiKeys ""

    foreach apiKey $apiKeys {
      #
      # NOTE: Issue the lookup request to the remote package repository.
      #
      set data [getLookupData $apiKey $package $version]