"Feature tags" only for required or also for optional features?

Question

Should "feature tags" (is there a better name?) like OS (linux, osx, windows, …), license (open-source), and costs (free) only be used if they are required features?

Or may they also be used for optional features?

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Example 1

The question Desktop Publisher (Alternatives to InDesign) is tagged with free and open-source (which would be valid combination, as Open-Source software must not be available for free). But in the question it says:

Cost/Licence: Must be free, Ideally would be Open Source

So here free is required, while open-source is optional.

(Same case with the question Free alternatives to Matlab that run on Linux?.)

Example 2

The question Free reference management software with full-text support is tagged with windows and web-apps. But in the question it says:

Target environment: Windows desktop or web

So here not both must be true (web-apps running on a Windows server; or being available cross-platform), but only 1 of 2 is required.

Example 3

The question Music manager for a mass storage based music player is tagged with windows and linux. But in the question it says:

I'm running Windows 7 and 8 mainly, so I would prefer windows, but I would accept a Linux based solution if nothing else is as good.

Here the software doesn’t have to be cross-platform, it’s either Linux or Windows (or both).

Answer 1

Tags are not really for features. Features are usually too precise for a tag.

Tags on this site should be mainly about application domains or domains of expertise. For example, windows, text-editors, math, …

Tags like free are still being debated, and definitely shouldn't be applied if the characteristic is optional — you shouldn't find non-free answers when you browse the free tag!

Answer 2

In my opinion, they should only be used for required features.

So in the example question, the tag open-source should be removed. The OP only requires that the software must be available for free, so users might answer with proprietary and with open-source software anyway. That the OP prefers open-source software can of course still be mentioned in the question text.

Otherwise, filtering by tag would lose much of its potential. When I filter for open-source, I expect that all answers recommend open-source software, nothing else.

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EDIT (new examples added to question):

For example 2 and example 3 it would mean that both of the OS/platform tags should be removed. So the OS requirements are only mentioned in the question/title, but not in the tags anymore.

When I’m filtering by linux, I expect that all answers recommend software that runs on Linux.

Only use an OS tag if the recommended software MUST run on this platform.

Answer 3

I think the tags should be used to requirements.

As you pointed out in the first example:

Cost/Licence: Must be free, Ideally would be Open Source

the tag usage would be free and the open-source would be removed, because it's optional.

On the second and third examples:

the tags windows, web-apps and linux would be removed. Because the requirement is not based on the system itself (but the software must run in a determinate system).

There should be created a tag with a name like os-required for the second example that shows that the OP wants a specific platform.

The tag cross-platform doesn't fit any of the examples above. But it should be used when needed.