Great question. Custom properties are displayed in the Custom Properties
window and dialog, so this information can be seen and changed by users
without having to dig into the Shapesheet. Custom properties also have more
cells in each row that allow for data type definition, labeling and
formatting of values. Many Visio features integrate with custom properties.
User-defined cells are unfortunately misnamed because they aren't visible to
users at all outside of the Shapesheet. These cells are typically used to
add behaviors to shapes to make them "smart". They can also store simple
data that should not be exposed to the user.
Look at the Shapesheet for an Organization Chart position shape to see a
good example that uses both Custom Properties and User-defined cells.
--
Mark Nelson
Office Graphics - Visio
Microsoft Corporation
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