Species Type: Character Set after "other:"

[s9105947]

To specify custom species, the species Type extension allows: "user are free to append a free text after a colon". Is really any text allowed? (What even is text?)

IMO "free text" should be severely restricted, at least to "printable characters without semicolon (;)". notable cases:

• semicolons ";" -> already is species list separator
• colons ":" -> is separator after "other" (though probably harmless)
• apostrophe (') and quotation marks (")
  • are generally annoying to escape
  • might be re-written by editors to use their UTF8-versions (“ ” ‘ ’)
• backslash \
  • is equally annoying to escape
  • is sometimes used to write control characters, e.g. \\n or \\a
• whitespaces -> sometimes annoying to handle, but generally safe
  • in order of [difficulty|annoyingness] to handle: spaces < tabs < newlines
• control characters -> influence display
  • ASCII? (e.g. nul, form feed, carriage return, backspace, bell)
  • UTF8? (e.g. byte order mark, right to left text indicator)
• non-ascii in general
  • e.g. anything non-english (e.g. german, russian, arabic, chinese)
  • (UTF8 is endless, see also: emojis, skin-tone modifiers, single flag characters, greek question mark etc.)
• pedantic is a character set even specified? are obscure iso-charsets allowed?
• empty string (entire name would be "other:")

By gut instinct I'd suggest to allow only "universally" safe and unambigous characters after "other:":

• only ASCII encoding (possibly already fixed by type "string", I have not checked)
• any number of characters from any number of these classes:
  • letters a-z (either case)
  • digits 0-9
  • one of: dash "-", plus "+", underscore "_", period ".", number sign "#", caret "^"
• excluded by design:
  • ";" b/c it is the list delimiter
  • "," b/c it could be confused for a list delimiter
  • whitespaces (space, tab, newline) b/c they tend to be difficult to handle or form special cases
  • backslash, apostrophe, quotation mark b/c they are annoying to escape

[ax3l]

To specify custom species, the species Type extension allows: "user are free to append a free text after a colon". Is really any text allowed? (What even is text?) IMO "free text" should be severely restricted, at least to "printable characters without semicolon (;)".

Correct. Derived from the base standard, we always mean pure ASCII when we write text. Yes, generally we leave other: unspecified for cases we have not yet thought about and that get standardized in later versions. A semicolon is also fine in that case, maybe someone things of another compound or list and wants to use the same convention. When it gets standardized later one, we only drop the other:, making file conversions easy. Thus,; are fine here.

I would not pro-actively allow <a-type-that-we-already-define>;other:<someStuff> yet, since I think we have no use case for this yet and it just complicates the syntax & conventions. (Unless you have a concrete case you need to achieve right now, of course.)

[s9105947]

Thank you for the clarification on ASCII, I overlooked that ._. I like the concept of reserving other: for entirely custom types and forbidding it from lists

So if I understand you correctly, a speciesType is:

1. one of the pre-defined species (fundamental particle, atom, maybe ion/molecule)
2. a list formed by multiple of those conforming to 1., separated by a single ";"
   • empty lists are forbidden
   • empty list items (containing ;;) are forbidden
   • trailing semicolons must be ignored
3. a string beginning with other:, followed by see below

Correct, so far?

This would leave these questions:

1. should empty strings after other: be permitted?
2. can a newline ever follow after other:?
3. which other characters are allowed?

I'd suggest: yes, no, class "print" of POSIX locale (IEEE 1003.1-2008, s. 7.3.1, l. 4187) 123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\]^_abcdefghijklmnopqrstuvwxyz{|}~ (+backtick ` +space +horizontal tab)