Every survey has a unique identifier that starts with the letter s and then some numbers an underscore and some more numbers. For example:
This identifier can be used to look up data in that survey such as by using the search function to get a list of choices for a survey using data from another survey. The survey identifier does not change if a survey is edited using the online editor or replaced by another XLSForm survey.
To get the identifier for a survey open the survey in the online editor and select the menu File and then Info. The survey identifier will be one of the values shown in a dialog.
The special identifier self can also be used wherever the survey identifier is used. self refers to the current survey. This is useful for looking up data that has previously been collected by the survey that you are using.