Re: Repetition syntax

If we're feeling skittish about the XML meanings of @ and angle-brackets I'd expect we'd also feel skittish about the ampersand's XML use to indicate entities.

XQuery manages to use () for sequence and (::) for comments; I don't know if this is bitterly regretted by the folks who have to implement it, but I would have expected { and *char*{ would be sufficiently distinct.

If we're willing to give up on the "US keyboard" assumption, it's not obvious we couldn't use «» for ranges. (U+00AB LEFT-POINTING DOUBLE ANGLE QUOTATION MARK and U+00BB RIGHT-POINTING DOUBLE ANGLE QUOTATION MARK in case the MTA mangles them.) (And more generally, Unicode is rife with brackets.)

On Mon, Dec 1, 2025, at 16:25, Bethan Tovey-Walsh wrote:
> I don't think we can use curly braces to delimit the range without running into serious problems, since curly braces are used for comments. 
> 
> I agree about the problem with "@". I've proposed using "&" instead, in a comment on the GitHub pull request. Why do you say that "&" is not available?
> 
> BTW
> 
> 
> ****************************************************
> 
> Dr. Bethan Tovey-Walsh
> 
> _linguacelta.com_
> 
> Golygydd | Editor geirfan.cymru
> 
> Croeso i chi ysgrifennu ataf yn y Gymraeg
> 
> 
>> On 1 Dec 2025, at 20:55, Graydon Saunders <graydonish@fastmail.com> wrote:
>> 
>> If I go look at https://invisiblexml.org/1.0/ixml.ixml.html and presuppose a US keyboard, we've got !, $, %, and \ currently not allocated as well as < and >. (Accepting that & and # are not available.)
>> 
>> I'd prefer to go with a variant on Liam's proposal of %{a,b} and %%{a,b} since @, like < and >, have deeply established meaning in XML context and it might be preferable to distribute the multiple uses more widely than ( and ).
>> 
>> But I don't find myself in the grip of strong opinions about this.
>> 
>> On Mon, Dec 1, 2025, at 11:13, Norm Tovey-Walsh wrote:
>>> Hello,
>>> 
>>> I think the idea of introducing repetition[1] into Invisible XML has been well received, there just remains the tricky and somewhat subjective question of what syntax to use.
>>> 
>>> In retrospect, it’s a real shame that we used up single “{“ and “}” for comments. But we did, that’s water under the bridge.
>>> 
>>> I propose <a,b> and <<a,b>> (parallel to * and **, and + and ++). I think it’s nice to delimit the beginning and the end, so a pair of brackets seems suitable. We can’t use (), [], or {} because those already mean something else. And we can’t use “#” as a delimiter because of hex escapes[2].
>>> 
>>> I think a single character could work: /a,b/ and //a,b//, for example, but it doesn’t strike me as obviously better.
>>> 
>>> Liam proposed @(a,b) (and, I assume, @@(a,b)). I think that could work too.
>>> 
>>> Any more suggestions?
>>> 
>>>                                         Be seeing you,
>>>                                           norm
>>> 
>>> [1] https://invisiblexml.org/pr/326/autodiff.html
>>> [2] I mean, technically, I think we probably *could*. I don’t think it would be ambiguous in the grammar, but I think it would be a mistake to make "a"#3 and "a",#3 both be legal and mean very different things. It feels like an invitation to error.
>>> 
>>> --
>>> Norm Tovey-Walsh
>>> Saxonica
>>> 
>>> 
>>