Nearly all documents are organized into sections, and even novels have chapters. Specifications are not novels and require more structure.
The classic software standards (eg IEE guidelines for the documentation of software in industrial computer systems) have suggested sections.
But modules are something more than sections as they fit into a model.
Often the process descriptions are written using Sectioning to represent the S88 models, for example
Equipment Module SubSection
But please note - the process of S88 segmentation - dividing the application into the various S88 modules (such as equipment modules) - is not something that can be done completely in defining the user requirements, although it is possible to make a start. At least identify the Units and Unit Procedures
Detailed Functional Requirements are best defined using a Requirements Model
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