docs

Author: fglock

FEATURE_MATRIX.md

@@ -253,6 +253,7 @@
 - ✔️   **Special variables**: The special variables `%ENV`, `@ARGV`, `@INC`, `$0`, `$_`, `$.`, `$]`, `$"`, `$\\`, `$,`, `$/`, `$$`, `$a`, `$b`, `$^O`, `$^V` are implemented.
 - ✔️   **I/O symbols**: `STDOUT`, `STDERR`, `STDIN`, `ARGV`, `ARGVOUT` are implemented.
 - ❌  **Thread-safe `@_`, `$_`, and regex variables**: Thread safety for global special variables is missing.
+- ❌  **Alternative ways to set typeglob**: `$constant::{_CAN_PCS} = \$const`.
 
 ## Perl Modules, Pragmas, Features
 - ✔️   **UNIVERSAL**: `isa`, `can`, `DOES`, `VERSION` are implemented. `isa` operator is implemented.