The bugs being referred to are from optional brackets in C: void foo() { ... if (expr) doA(); doB(); ...

The bugs being referred to are from optional brackets in C: void foo() { ... if (expr) doA(); doB(); ... } which is unambiguous to the compiler, but could (and I expect would, especially when glancing through a lot of code) cause misinterpretation by a human reader. We can more easily hallucinate the brackets than the indentation. I disagree with the idea that indentation spaces are invisible; rather they are much more visible than a pair of brackets. This actually becomes a problem when you embed/indent too much and 70% of the line is spaces. It's all you see!