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A convention for gemlog tags

i'm not aware of any widespread convention for designating tags on a gemlog post - if there is one, please let me know! Otherwise, at the risk of creating standard 15[a], here's what i'm going to start using on my own gemlog.

Definition

1. A ‘tags line’ is designated with the character ‘🏷’ at the beginning of a line,

2. optionally followed by

3. at least one space and/or tab, and

4. a comma-separated list of values,

5. each value containing any valid UTF-8 character above and including codepoint 0x20,

6 with the exception of a comma (‘,’).

7. The line may contain a trailing comma.

8. The list of tags cannot extend past the end of the line beginning with ‘-<=’.

9. In the presence of more than one tags line in a document, the last line wins.

Commentary

1. When this post was first published, line 1 referred to “the three characters ‘-<=’”, and this line of commentary originally said “the trigraph ‘-<=’ is intended to look vaguely like a physical tag, and seems reasonably unlikely to be regularly used for another purpose within gemtext.” The line prefix was changed to ‘🏷’ as a result of feedback.

2. Making everything after these three characters optional allows for the possibility of having a ‘placeholder’ tags line.

4. Field splitting on commas is trivial in any serious programming language[b].

6. Allowing a trailing comma is intended to make it easier to generate a conformant tag list.

6. Having the tags line be no more than a single line is intended to facilitate line-oriented parsing.

8. The “last line wins” rule is intended to handle faulty gemtext generators (which in some instances might be a human brain).

Example regular expressions

The final inner parenthesis group in each example represent a capture group, which can then be split on ‘,’.

PCREs

man page: ‘pcre2syntax(3)’

^-<=(?:(?: |\t)+([^\n]+))$

ELisp REs

Emacs Lisp Reference Manual: ‘35.3.1 Syntax of Regular Expressions’

^-<=\\(?:\\(?: \\|\t\\)+\\([^\n]+\\)\\)$

POSIX.2 EREs

man page: ‘regex(7)’

^-<=(( |\t)+([^\n]+))$

Test data

A tags parser must parse the test_tags.txt file as follows:

The first four lines must not be recognised as valid (extraneous whitespace).
The last seven lines must be recognised as valid.

test_tags.txt

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Glossary

Gemlog Home

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[a] xkcd: ‘Standards’

[b] i.e. i'm not particularly concerned about esolangs like Ook! or Piet. :-)