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I think 20 columns in an editable grid is just not a good idea. What is the use case?
Agreed - to me, more than a small handfull of editable columns almost always ends up meaning it's better to require the user to select the entry from a read-only grid and edit the data in its own little section with the appropriate fields, and when a new row is required, have them use a button/link/etc to allow entry of new data via the same section but with blank values.