When you run an update operation without any option on a url (buku -u), the data are retrieved from the remote site and overwrite the preexisting fields (title, comment) or append them (tags).
However, you sometimes only want to update specific fields and preserve the others that are already present from any modification. For instance after an import of your bookmarks tagged with your own keywords, you only need to refresh titles and comments but don't want to append your own tags with other fetched tags.

It would be useful to allow such behaviour with a new command line option on the update operation (--preserve).

Here are some details:

• --preserve prevents any automatic modification on each specified fields (title, comment, tags). For instance buku -u 10 --preserve comment should only append tags and and update title and should not affect the comment
• arguments of the --preserve option could be combined with commas to specify which field should be preserved (i.e --preserve title, tag)