Use Metadata where possible
Some file types have their own metadata format, like XMP in PDF or EXIF in images. It would be nice, if the metadata fields would be used for tagging, if possible. Renaming files is a quite nice mechanism but could lead to errors if, for example, files live in a version control system.
Duarte Farrajota Ramos commented
I am not sure if this is possible or if it might have undesirable effects, but wouldn't it be possible to save those same tags inside the file for text based file formats like HTML, python, xml, php watever?
I mean I they are text based files so perhaps at the end of that file create some sort of section where tagspaces metadata would be saved. I know this could break some file's structure or render them unusable/corrupt in their own functions. Perhaps come up with some syntax that would read as a comment or get ignored in most languages? For HTML this would most likely not be a problem.
For the rest of the non text based use their correspondent common tags like ID3, Exif, PDF, etc., or if non available use an existing standard like XMP with xmp sidecar files. These could even be made "invisible" inside tagspaces and get copied/moved/renamed along with their corresponding file automatically without further user intervention.
Although this approach is only working with special filetypes it has the advantage, that standard viewers for that filetype could also display the tags set to the file. So perhaps a "double approach" would be the best way... although how to automatically synchronize them?
Max Pittsley commented
This would leave out several filetypes, like text-based file formats. I think this suggestion is probably a better approach: <https://tagspaces.uservoice.com/forums/213931-general/suggestions/5789542-save-tag-data-and-metadata-in-a-separate-file>