Slice operator is marked as invalid

[fionera]

This is a valid expression:

strings.Join(_t[:len(_t)-1], "-")

[jansorg]

intellij-cue/src/grammar/cue.bnf

Lines 197 to 204 in 66d45bf

	// fixme this is a simple rewrite as non-left-recursive for now
	// fixme: commented slice as it's not yet well defined in the grammar
	PrimaryExpr ::= Operand {Selector | Index /*| Slice*/ | Arguments}* {extends=Expression}
	Selector ::= "." (<<identifier_ref>> | simple_string_lit) {extends=PrimaryExpr}
	Index ::= "[" Expression (":" Expression)? "]" {extends=PrimaryExpr pin=1} //fixme find out why example use ":" in Index
	Argument ::= Expression {extends=PrimaryExpr}
	Arguments ::= "(" [ ( Argument { comma Argument }* ) [ comma ] ] ")" {extends=PrimaryExpr pin=1}
	// fixme Slice is missing

, the official grammar is missing the spec of Slice. Is there perhaps a list of examples to help me understand what it does?
I'm not a regular user of Cue, so I don't know enough about the language to fix it without a spec.

[jansorg]

cc @leoluk ^

[fionera]

Afaik its the same grammar as in Go