Every object by default contains no custom properties, but you can add them to an object to store values.
You can add or change a property using the property inspector window or through script code.
set the mycustprop of me to "Hello world"
Custom properties are fundamental in LiveCode, and can change the way programmers code. The idea of linking the data with the object using it is productive.
If you don't need the custom property for an object anymore, you can delete it and also all of the objects other custom properties. This way the software doesn't continue to store unnecessary data. It allows it to be clear where the data is, and why.
You can see and edit custom properties visually with the property inspector: as well: