The Help page, What are tags, and how should I use them? states vaguely:
How to format tags
…
Avoid punctuation (which can make it difficult to use the tag in a URL)
Does this mean I should not use a dot/period/FULL STOP/. character in my tag name?
Some technical product names use a period. For example, see this meta page discussing a tag name for the java.time framework.
I do recall being told years ago to delete a tag java.time and creating a tag java-time. I then volunteered to reassign the tag to dozens of questions. This issue is not that Stack Overflow prevents the creation of a tag with a dot; clearly we can. The issue is whether we should or should not use a dot in a tag.
And by the way, I suggest that Help page be edited to be specific about prohibited characters.
.,+, and#are specially handled and can be used.-works normally. Other punctuation should be avoided. Thejava.tagdiscussion is about merging two tags with the same meaning, not about the punctuation.java.timeand creating a tagjava-timeand then volunteering to reassign the tag to dozens of questions. This issue is not that Stack Overflow prevents the creation of a tag with a dot, clearly we can. The issue is whether we should use a dot in a tag.., but about consistency. Every Python function or library is taggedpython-*, every Java function, etc., should be taggedjava-*, every jQuery plugin is taggedjquery-*, even though some of them contain a.in actual code.t-cçç, the C# questions have the class namet-cñ, and .NET questions have the class namet-ûnet. There’s also an answer mentioning this somewhere on Meta that I’m trying to find.-(hyphen) are treated as-is, meaning that the user has to explicitly type the character to include it in the search result, compared to-which is basically ignored, e.g.javat(without hyphen) also returnsjava-time, but onlyjava.t(with dot) returnsjava.time.