The Perl policy document points out that certain features are designated as "deprecated", "discouraged", or "removed" within the core Perl:
$[ which makes strings and arrays be 1-based instead of 0-based (deprecated in v5.12.0, fatal error in v5.30.0)use vars instead of our (discouraged in v5.6.0)$# which could be used to format printed numbers (deprecated in v5.0, removed in v5.10, fatal error in v5.30)$* which could be used to enable multiline matching (deprecated in v5.0, removed in v5.10, fatal error in v5.30)