cue: compile builtins at init time
Also allow any CUE as literal value for builtins.
This, in turn, is necessary to define some useful core
types (like time.Time) as well as to give better support
for the scripting layer, allowing better abstractions
for tools.
Updates #24
Change-Id: Icdcf7dfe7330bcc0efef437689503a84bcf3567c
Reviewed-on: https://cue-review.googlesource.com/c/cue/+/1721
Reviewed-by: Marcel van Lohuizen <mpvl@google.com>
diff --git a/doc/ref/spec.md b/doc/ref/spec.md
index 4f5783b..6ea7707 100644
--- a/doc/ref/spec.md
+++ b/doc/ref/spec.md
@@ -1108,12 +1108,12 @@
An identifier or string label may be followed by a question mark `?`
to indicate a field is optional.
+The question mark is not part of the field name.
Constraints defined by an optional field should only be applied when
a field is present.
-Fields with such markers may be omitted from output and should not cause
+A field with such a marker may be omitted from output and should not cause
an error when emitting a concrete configuration, even if its value is
not concrete or bottom.
-The question mark is not part of the field name.
The result of unifying two fields only has an optional marker
if both fields have such a marker.
