Apply-scripts are unreadable and hard to maintain. The language of choice for larger proofs is Isar. The two key features of Isar are (1) It is structured, not linear. (2) It is readable without its being run because you need to state what you are proving at any given point. Whereas apply-scripts are like assembly language programs, Isar proofs are like structured programs with comments. A typical Isar proof looks like this.
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