Thinking more...

IEEE Standard 830
IEEE recommended practice for software requirements specifications
A good example: http://www.fsai.fh-trier.de/~federhen/dippaper/docu/11_Software_Requirements_Sp.html

In "Software Requirements - MS Press", Page 155
1. Introduction
1.1 Purpose
1.2 Document conventions
1.3 intended audience and reading suggestions
1.4 project scope
1.5 references
2 overall description
2.1 product perspective (展望,roadmap)
2.2. product functions (一般以條列為主)
2.3 user classes and characteristics (誰會用這產品)
2.4 operating environment
2.5 design and implementation constraints
2.6 assumptions and dependencies (可能會用到的 library/components...)
3 external interface requirements
3.1 user interfaces
*GUI standards or product family style guides that are to be followed
*Screen layout or resolution constraints
*standard buttons, functions, or navigation links that will appear on every screen( such as help button)
*shortcut keys
*error message display standards
more details can be describe in a separate user interface specifications, not here.
3.2 hardware interfaces
3.3. software interfaces
the interfaces which export to other software or component
3.4 communications interfaces
4. system features
organize this section by use case, mode of operation, user class, object class, or functional hierarchy.
4.x system feature X
4.x.1 description and priority
4.x.2 stimulus / response sequences
4.x.3 functional requirements
5. other nonfunctional requirements
5.1 performance requirements
5.2 safety requirements
5.4 software quality attributes
5.5 business rules
5.6 user documentation
6. other requirements
appendix a: glossary
appendix b: analysis models
appendix c: to-be-determinded list