Interactions between document parts.

This category is home to Typst's introspection capabilities: With the `counter`
function, you can access and manipulate page, section, figure, and equation
counters or create custom ones. Meanwhile, the `query` function lets you search
for elements in the document to construct things like a list of figures or
headers which show the current chapter title.

Most of the functions are _contextual._ It is recommended to read the chapter on
[context] before continuing here.
