Sequential Coding for Heading Tags: Headings for a series of windows must always start with :h1. and proceed in sequence. That is, you cannot have :h1. followed by :h3.. However, you can follow :h3. with :h1..
Source File Size between Heading Tags: Do not exceed 16 000 words, numbers, and punctuation marks between two consecutive heading tags in your source file. This includes blank spaces, but does not include commented lines (see Comment). If the source file exceeds this limit, the compiler will generate an error message. To correct the error, use another heading tag.
For more information about heading tags and attributes that define characteristics of windows, see Customizing Windows.
Note: At least one :h1. must not be hidden.