Another division is a <worksheet>. It is similar to a <chapter>, <section>, and so on, but with some variations to support a worksheet or in-class activity. Here we recognize the primacy of printed output (perhaps to bring into a classroom), and the online version is a less-capable representation.
There is no limit to what you can place in a <worksheet> division: objectives, an introduction, theorems, figures, images, and so on. But the principal element is an <exercise>, which mostly behaves like an <exercise> in an <exercises> division, but with additional capabilities.
An <exercise> in a <worksheet> can have a specified width when included in a <sidebyside>, and in any case may have a specified additional blank working space of specified height. Page breaks can be specified, and the four margins on a page can be independently controlled. So if you want to create ancillary worksheets for your project, and you like to use all of the space on a printed page, then there is some layout control to support that.
Notice that all of this layout control is an exception to the philosophy of PreTeXt. So in particular, margins and working space do not appear in the HTML output. We do give a visual indication where a page break in a <worksheet> is placed. An author might wish to collect all of the worksheets in a book, for printing as an “activity book”, and so there are plans (2018-08-11) to support and automate that process. Details for authoring worksheets can be found in Section 6.3.