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Please do keep in mind that it is important to not confuse the form data with workflow variables. As explained before, they are separate entities but both entities can be used as hash variables for use inside, for example, an email body.
Scope of Use
Please note that every hash variable has its scope of use. This dictates where the hash variable can be used. Workflow variable hash variable(#variable.variableName#), can only be used by elements within and part of a Process.
Additionally, these values are being parsed on the server side, not the client side. If there is a need to parse it, you will need to use workflowutil.processVariable method to do so.
Update Mechanisms
Form Data Update Tool: This built-in tool is used to update values directly in the database. To use this go to Process Builder > Tools > Mapping > Select Update Form Data > Update Fields.
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