To insert a link to an Abinit variable, use:
{{ecut}}
or:
{{asr_anaddb}}
if you want to refer to the asr variable of the anaddb code (note that in abimkdocs one uses asr@anaddb but, unfortunately this syntax is not supported my MyST).
There are several other replacements defined in _config.yml, mainly for links to the abipy documentation, python libraries and other useful websites. Also in this case, the syntax is:
{{replacement}}
The snippets directory contains (well) snippets that can included in the md file with the syntax:
```{include} snippets/abicheck_warning.md
```
Note that the path of the include file is relative to the document.