XLSForm spec proposal: add syntax to make it easy to use a value from the last saved instance

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EDITED to use last-saved instead of last as the prefix.

How have the latest ideas aged through various showers/sleeps/brain marination sessions?

Here is what I think the latest proposal looks like:

  • If the contents of the default column are not a literal value, the expression is passed through to the value attribute of the setvalue action (see documentation) triggered on first load (using the odk-instance-first-load event). Literal values get treated the same way they do now.
  • Introduce new syntax to refer to a question in the last instance: ${last-saved#<question_name>}
    • If an XLSForm definition uses this construct, <instance id="__last-saved" src="jr://instance/last-saved" /> will be added to the XForm
    • ${last-saved#<question_name>} will expand to instance('__last-saved')/data/question_name (with additional group/repeat levels as needed -- same as with the ${<question_name>} construct).
survey type name label default
text street Street ${last-saved#street}
date disaster_date Disaster date today()
integer patient_count How many patients have you seen today? if(${last-saved#patient_count} == '', 0, ${last-saved#patient_count} + 1)
select_one yes_no same_street Are you still on ${last-saved#street}?

This:

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