doc/ref/spec.md: fix len count for structs
Fixes #344
Change-Id: Iaef0b2e55786fab365f6ef867b877ceeb7663092
Reviewed-on: https://cue-review.googlesource.com/c/cue/+/7081
Reviewed-by: Marcel van Lohuizen <mpvl@golang.org>
diff --git a/doc/ref/spec.md b/doc/ref/spec.md
index 8d7f2eb..ca9df9f 100644
--- a/doc/ref/spec.md
+++ b/doc/ref/spec.md
@@ -2647,7 +2647,7 @@
string string length in bytes
bytes length of byte sequence
list list length, smallest length for an open list
-struct number of distinct data fields, including optional
+struct number of distinct data fields, excluding optional
```
<!-- TODO: consider not supporting len, but instead rely on more
precisely named builtin functions:
