diff --git a/docs/missing_features.md b/docs/missing_features.md
index 7926408..b819fec 100644
--- a/docs/missing_features.md
+++ b/docs/missing_features.md
@@ -16,6 +16,10 @@ identified as necessary for a complete language specification.
 - Constants
 - Arrays of structs
 - Arrays of non-default types
+- Identifiers can be any ascii (or possibly unicode) string without whitespace,
+that doesn't start with a digit (`0-9`), `.`, or `:`, and doesn't include `::`
+- Integers and floats are allowed to use `_` as deliminator, they are ignored
+after lexing, they are just for the programer
 
 ### Arrays of non-default types and structs