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-rw-r--r--README.md1
1 files changed, 1 insertions, 0 deletions
diff --git a/README.md b/README.md
index 1be1677..7057611 100644
--- a/README.md
+++ b/README.md
@@ -171,6 +171,7 @@ Default: `n`.
 	             | =~~               -- case insensitive POSIX Extended Regular Expressions
 	
 	<str>      ::= " ([^"] | "")+ "  -- use "" for a single " inside "
+	             | $[A-Za-z0-9_]     -- environment variable
 
 	<typetest> ::= type ( == | = | != ) ( b | c | d | p | f | l )