Which functions should preserve objects' attributes?

~~Currently the only function that preserves a selected subset of the input object's attibutes is stri_sort~~ (see #63)

Which other functions should preserve the attributes?
Which attributes should be preserved (names, ...)?
If there are > 1 parameters, what shall be the attribute selection strategy?

Start by reviewing issue #63 and the current stri_sort behavior, which is the only preservation case mentioned. Determine which functions and object attributes are in scope and how multiple parameters should be handled; the issue is complete only after those preservation rules are agreed and documented.

Written by the indexing model from the issue text.