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DI) characters can lead to incomprehensible code.

The Unicode encoding contains BIDI control characters that are used to display text right-to-left (RTL) instead of left-to-right (LTR). This is necessary for certain languages that use RTL text. The BIDI characters can be used to create a difference in the code between what a human sees and what a compiler or interpreter sees. An advisary might use this feature to hide a backdoor in the code that will not be spotted by a human reviewer as it is not visible.

This can lead to supply chain attacks since the backdoored code might persist over a long time without being detected and can even be included in other projects, for example in the case of libraries.