EBNF - Allow special sequence management with special-sequence-symbol "?"

Question

Hello PlantUML team,

• Could you allow special sequence management with special-sequence-symbol "?"?

Here is some examples (taken from the ISO EBNF standard):

@startebnf
(* Example from §8.1 ISO-EBNF *)

h-tab = ? IS0 6429 character Horizontal Tabulation ? ;

new-line = { ? IS0 6429 character Carriage Return ? },
? IS0 6429 character Line Feed ?,
{ ? IS0 6429 character Carriage Return ? };
@endebnf

or:

@startebnf
(* Other possible examples: *)
h-tab = ?Unicode U+0009?;
empty-special = ??;
@endebnf

A proposal will be to make a double line around the block. (to debate...)

Thank for the improvement (not urgent, but just ISO EBNF consistent),
Regards.

Comments

In http://alphadoc.plantuml.com/doc/markdown/en/ebnf I added an ebnf defintion of ebnf...

A good practical example of how this may be used is digit, and letter... these could be replaced with:

digit = ? regex: \p{Number} ? ;

letter = ? regex: \p{Letter} ? ;

As I am going to assume we will allow any numbers/letters, not just english ones.

Alternatively:

digit = ? regex: [0-1] ? ;

letter = ? regex: [a-z] ? ;

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I think this is enough to release ebnf in the same way the alternative "beta activity diagrams" are.

I would release it into the wild for public comment for a bit and emphasize its in beta... I am sure ebnf people will jump on this once released... although I do it from time to time I am more of a java guy, so the public may be a better sounding board for suggestions at this point.

Should we turn to documentation for what we have?

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To complete this I would suggest changing special to one or more of...

More then the double line (it's just not distinct enough I think, so solid and broken lines or something)

Distinct background color (yellow it already used for comments... Blue maybe?)

Add some kind of indicator or icon (something like the slash on business actors?)

Use a non rectangular block around it (see cloud symbol in deployment diagrams for example)

Wobbly lines might also work.

It's not horrible as is (so if others disagree I will drop this), just think it needs a bit more panache.

What ever one of these is easiest to implement on top of what you have is what I would do

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I think if we use the dashed version of the UStroke for one but not both rectangles... new UStroke(1.0,1.0,1.0)??, we would have something easy to understand at a glance... the numbers might need tweaked a bit.

https://github.com/plantuml/plantuml/blob/48ae51e8c3ee3cd5713834350f682b086db208d8/src/net/sourceforge/plantuml/ebnf/ETileBox.java#L160

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I think this can be closed

Answer 1

With last version, you can have:

Does it make sense?

Comments

For me that seems good...

Conform to my initial request:
> A proposal will be to make a double line around the block. (to debate...)

Thanks a lot.
Awaiting now 'exception management'...
Regards.
Th.

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Sure does, you got the concept exactly... a bit hard to see... any way to make the lines bold or something? Its simply those should not look the same as the others... how IDK, but they should be visually distinct.

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never mind... forgot about the grey for normal nodes... with thse being white I think its fine!

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oops... it should not look like rules, nor literals.

https://www.plantuml.com/plantuml/uml/SoWkIImgIKtAI-DAoyzNi5LGoiaiIIrAp55Ig56mBov8JSvCpB47iejASrAjkHnIyr90YW40

All 3 elements should be visually distinct. Literal and special look very similar.

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Specials should look "funky"... a lot of books and such use another color (yellow is common), or bold text, borders, and even sometimes drop shadow... etc.

Basically specials should NOT look like a normal item... its "special". ;-) bad pun

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How about one solid and one dotted line?

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one solid and one dotted line?

Why not?
It seems a good new improvement... (conform to the spirit of `special`)

---

I think if we use the dashed version of the UStroke for one but not both rectangles... new UStroke(1.0,1.0,1.0)??, we would have something easy to understand at a glance... the numbers might need tweaked a bit.

https://github.com/plantuml/plantuml/blob/48ae51e8c3ee3cd5713834350f682b086db208d8/src/net/sourceforge/plantuml/ebnf/ETileBox.java#L160

Answer 2

This might close https://forum.plantuml.net/16693/ebnf-add-notation-elements-as-rules IMHO
I would suggest making this as close to other formats while correctly processing "standard EBNF" so I like all suggestions