Example 6.23 and 6.24 in YAML 1.2 spec dated 2009-07-21

Dear the YAML spec writers,

Regarding to the YAML 1.2 spec dated 2009-07-21:

I struggled for long time to reproduce example 6.23 and 6.24. 
because the rule for s-l+block-collection(n,c) requires 
intra-rule rewinding to accept them.

For instance, when s-l+block-collection(-1,block-in) try matching
to the input of the example 6.23, at first "!!str &a1" is reduced
by ( s-separate(n+1,c) c-ns-properties(n+1,c) )? and then 
s-l-comments fails to match. Usually, this results in the whole 
s-l+block-collection(n,c) fails to match. Here, however, it 
must also try the case "!!str &a1" is *skipped* by 
( s-separate(n+1,c) c-ns-properties(n+1,c) )? , in order to 
successfully accept the example by following l+block-mapping(-1).

I think it is clearer to have separated rules for the block 
collection with properties and that without properties.
The following is my suggestion.

s-l+block-collection(n,c) ::= s-l+block-collection-with-properties(n,c)
                            | s-l+block-collection-without-properties(n,c)

s-l+block-collection-with-properties(n,c) ::= 
             ( s-separate(n+1,c) c-ns-properties(n+1,c) )?
             s-l-comments
             s-l+block-collection-without-properties(n,c)

s-l+block-collection-without-properties(n,c) ::= 
                   l+block-sequence(seq-spaces(n,c)) 
                 | l+block-mapping(n) 

Osamu Takeuchi

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