Further reading

In the TikZ manual, available at https://texdoc.org/pkg/tikz in PDF format, these sections are relevant:

• Part III, Section 15, Actions on Paths, is about filling, clipping, and shading, and it explains the interior rules concisely. The direct online link is https://tikz.dev/tikz-actions.
• Part V, Section 69, Shadings Library, is the reference for always-defined and additional shading types, and it can be found at https://tikz.dev/library-shadings. Part IX, Section 114, Shadings, explains the backend programming behind shadings and can help you to create your own shading, such as tuning a ball shading with different highlighting. It’s available online at https://tikz.dev/base-shadings.
• The web page https://www.w3.org/TR/SVG/painting.html#WindingRule by the World Wide Web Consortium (W3C) describes the nonzero and even odd interior rules from the point of view of the SVG standard.
• The TikZ galleries at https://tikz.net and https://texample.net...