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The most common problem with existing macros is an improper quotation. This section, which users of Autoconf can skip, but which macro writers must read, first justifies the quotation scheme that was chosen for Autoconf and then ends with a rule of thumb. Understanding the former helps one to follow the latter.
| • Active Characters | Characters that change the behavior of M4 | |
| • One Macro Call | Quotation and one macro call | |
| • Quoting and Parameters | M4 vs. shell parameters | |
| • Quotation and Nested Macros | Macros calling macros | |
| • Changequote is Evil | Worse than INTERCAL: M4 + changequote | |
| • Quadrigraphs | Another way to escape special characters | |
| • Balancing Parentheses | Dealing with unbalanced parentheses | |
| • Quotation Rule Of Thumb | One parenthesis, one quote |