Recorded scope and limits
RFC Editor publication, November 1987. Re-read preferred name syntax, case comparison and label-size context. The historical preferred syntax is not a complete current hostname rule: RFC 1123 later updates it. DNS labels, application hostname fields and URL components must not be treated as one validation target. No physical labeling requirement is inferred. Checked October 29, 2026.
Use the task guides below to see how this source informs a labeling decision. Check the publication scope and the edition adopted by your project before applying it. A publisher overview is not the full text of a standard, and software documentation does not prescribe a physical label format.
Read the library’s edition and applicability notes.
What this source establishes
Historical DNS naming context only, read with its later updates. This source does not establish a universal character policy for physical labels or URLs.
Review date: 2026-10-29. This note describes the source scope; it is not a project approval.