Source-Code-Links.md

@@ -24,6 +24,19 @@ following substitutions are made in the file template:
     {file} - The name of the file
     {line} - The decimal line number.
 
+_Note:_ The [current implementation](https://github.com/golang/gddo/blob/d5e22321f6d50a058e175b602f2cc55a66a62a18/gosrc/gosrc.go#L379-L390)
+imposes a few additional restrictions to the description above. In order for the file field to have an
+effect (and not have unexpected adverse effects), these rules must be followed until the implementation is fixed:
+
+- The file field URL template must contain at least one instance of `{file}`.
+- If a `#` is present in the URL template, all instances of `{file}` must come before the `#`.
+  All instances of `{file}` that come after `#` will not be substituted.
+- The `{line}` component is optional, but if it is to be included, then the file field
+  must contain `#` and the instance of `{line}` must be after the `#`. Instances of `{line}` that come
+  before `#` will not be substituted.
+- In order for `{line}` substitutions to be made, no more than one instance of `{line}` must appear in the file field after `#`.
+- It's okay for `%` to be present after `#`, but not before.
+
 The meta tag content attribute must contain four fields. Use "_" to fallback to
 GoDoc.org's defaults for home, directory and file.