Celtic Knotwork Borders in Repeating Sections is a collection of original Celtic knotwork border designs presented in a way that's meant to allow artists the freedom to create knotwork borders in virtually any size, and practically any shape, that they want.
The book uses a modular system in which a border design is reduced to either two or five straight sections, plus a variety of arc sections with different numbers of repeats around a full circle.
These sections are meant to be rotated as needed to form square, rectangular, or circular borders for use in your work.
Not only are there straight and corner sections for each pattern, but every one of them also includes circle sections in several numbers of repeats around a full circle.
Half of the designs also feature "inner border" variations. These are designed to branch inward from the main borders with T sections, and the inner borders can cross in the middle of the border with the provided crosspieces.
The book's approach is based on the author's experience of more than 25 years. It's intended to teach you to think about repeating patterns in a way that'll improve your own work - the idea is that the mechanical task of laying out a border should be streamlined, leaving you free to concentrate on the much more creative work of painting, carving, or dyeing it.
The text includes ideas on how to scale the patterns - they're printed here in many sizes, but it's inevitable that you'll want more - and that, and other information, is given for both digital and traditional artists.
You can use these designs in any way you like for your own work. You're completely free to sell that work, or reproductions of that work. You just aren't allowed to make a clip art collection out of them, or otherwise reproduce the pattern sections alone in a form that others can use.