To designate subprojects to be merged, list the subproject paths and titles. For example:
[HelpMerge] ; Subproject name and path = Title of subproject ..\api\LibRef = API Library Reference
Each [HelpMerge] entry specifies a subproject base file name, including a relative path if the subproject is in a different directory, and the title to be displayed for that subproject in the main-project contents. The relative path must be correct at run time.