In the continuity of [Software design principles applied to digital gardening](Software%20design%20principles%20applied%20to%20digital%20gardening.md), using the open-closed principle (the O of [SOLID](SOLID.md) acronyme) makes our system closer to the original [Zettelkasten](The%20zettelkasten%20method%20and%20how%20to%20take%20smart%20notes.md) system. By design, Luhmann's paper cards were closed to modifications but open for extensions, simply because of its physical aspect. Once the card is full, we just can't add more informations and can't modify or erase because of the ink, hence the obligation of extending it. This what make Luhmann's [Zettelkasten](The%20zettelkasten%20method%20and%20how%20to%20take%20smart%20notes.md) system so strong and profuse.