I have the following questions to ask related to Epicollect 5 use

Q1. Example of difference between Branch and Group variable
Q2. Example of using Regex only digits and Regex only Letters
Q3. Example of using Input Read me
Q4. Can we merge more than 3 childforms using VLook up function.
Q5. During mapping , when I am trying to update my file it mentions ‘got invalid identifiers’ , how to resolve this issue ? Please help with it.