nitdoc: Document constraints on `nitdoc_id`.

Signed-off-by: Jean-Christophe Beaupré <jcbrinfo@users.noreply.github.com>

diff --git a/src/doc/doc_model.nit b/src/doc/doc_model.nit
index 12fbf72..3a560f5 100644 (file)
--- a/src/doc/doc_model.nit
+++ b/src/doc/doc_model.nit
@@ -35,7 +35,15 @@ redef class MEntity
        # HTML Escaped name
        fun nitdoc_name: String is abstract
 
-       # Used as HTML unique ids
+       # ID used as a HTML unique ID and in file names.
+       #
+       # **Must** match the following (POSIX ERE) regular expression:
+       #
+       # ~~~POSIX ERE
+       # ^[A-Za-z_][A-Za-z0-9._-]*$
+       # ~~~
+       #
+       # That way, the ID is always a valid URI component and a valid XML name.
        fun nitdoc_id: String is abstract
 
        # URL of this entity’s Nitdoc page.