Any ZZT-OOP line beginning with an apostrophe (') is treated as a comment and ignored by the interpreter. Comments provide a way for the programmer to document their code, or to quickly disable lines of code without deleting the text.
Comments are used in the implementation of zapping and restoring labels.
The apostrophe must be the first character on the line. Any leading whitespace will cause the line to be treated as display text. Text placed after commands may be ignored in a manner similar to comments due to how the interpreter parses code lines.