What is the mutable part of the attribute properties?

The Tango::Attribute::set_properties doc says that only part of the attribute’ properties is mutable.

The question is: which part of the properties set is mutable?

I carefully read the 250+ pages of the Tango book _ but couldn’t find the info.

This post is not in the right section of the forum cause I’m reusing a “oops” post -_- If someone has the right privileges to change that…