Lines that start with a colon are metadata, for instance :for:[symbols_simple] indicates that the Example is for a mathematical theory called symbols_simple elsewhere in the document.
There are shortcuts for certain types of metadata, for instance double quotes following the colon :"The Title" for titles, ISO 639-1 language tags for the language, and then if the text after the colon is not a single token and has no colons it marks an author.
It produced XML with the language put in xml:lang attributes, that was later processed into HTML and LaTeX for each language, and from that into DVI, PS, PDF.
I chose to have the tags at the start for the reasons you mention. When having several of them together as in the example they form a visual block that I find easier to scan.
[1] https://matracas.org/qmath/
Lines that start with a colon are metadata, for instance :for:[symbols_simple] indicates that the Example is for a mathematical theory called symbols_simple elsewhere in the document.
There are shortcuts for certain types of metadata, for instance double quotes following the colon :"The Title" for titles, ISO 639-1 language tags for the language, and then if the text after the colon is not a single token and has no colons it marks an author.
It produced XML with the language put in xml:lang attributes, that was later processed into HTML and LaTeX for each language, and from that into DVI, PS, PDF.
I chose to have the tags at the start for the reasons you mention. When having several of them together as in the example they form a visual block that I find easier to scan.
The idea of using colon to mark these came from AsciiDoc: https://docs.asciidoctor.org/asciidoc/latest/attributes/attr...