_content/ref/mod: clarify that go.mod files are not required for dependencies
We already mentioned this fact elsewhere in the document, but the
"go.mod files" section is a likely starting point for someone trying
to figure out what happens when the file is missing. This adds some
prose and links there to point the reader to the appropriate sections.
Noticed via https://stackoverflow.com/q/67030123.
Change-Id: Ia7fe50a8b97b8cc1320778c318e5b3b0694d7c05
Reviewed-on: https://go-review.googlesource.com/c/website/+/331949
Trust: Bryan C. Mills <bcmills@google.com>
Run-TryBot: Bryan C. Mills <bcmills@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Jay Conrod <jayconrod@google.com>
diff --git a/_content/ref/mod.md b/_content/ref/mod.md
index 2e83597..cc20bc1 100644
--- a/_content/ref/mod.md
+++ b/_content/ref/mod.md
@@ -356,6 +356,13 @@
[`golang.org/x/mod/modfile`](https://pkg.go.dev/golang.org/x/mod/modfile?tab=doc)
package can be used by Go programs to make the same changes programmatically.
+A `go.mod` file is required for the [main module](#glos-main-module), and for
+any [replacement module](#go-mod-file-replace) specified with a local file path.
+However, a module that lacks an explicit `go.mod` file may still be
+[required](#go-mod-file-require) as a dependency, or used as a replacement
+specified with a module path and version; see [Compatibility with non-module
+repositories](#non-module-compat).
+
### Lexical elements {#go-mod-file-lexical}
When a `go.mod` file is parsed, its content is broken into a sequence of tokens.
