diff --git a/utils.capnp b/utils.capnp
index a5ec60b..c75bc8c 100644
--- a/utils.capnp
+++ b/utils.capnp
@@ -10,18 +10,25 @@ interface L10NString {
     get @0 ( lang :Text ) -> ( lang :Text, content :Text );
     # Retrieve the string in the given locale. The input parameter MUST be a RFC5646-formatted
     # locale identifier (e.g: "en-US", "de-DE", "az-Arab-IR").
-    # A server MUST set the outputs `lang` to the exact tag that the content it sends was written in
-    # and `content` to the localized string.
-    # If a server can't find a localized version it SHOULD try to substitute it. Substitution SHOULD
-    # only search for close matches, e.g. returning "en-UK" for a string requested in "en-US" or
-    # returning "es-ES" for a requested "es-VE". Substitution MUST NOT return a localization that an
-    # user can not be expected to understand unless the server has a priori knowledge that the user
-    # can read and understand said language.
-    # If a server sends a substituted string it MUST set the output `lang` to the tag of the
-    # substitute it is sending.
-    # If a server can't find a suitable substitute or is not doing substitution it MUST set the
-    # output `content` to a NULL pointer and set the output `lang` to the input `lang` it was
-    # passed.
+    # 
+    # If a server can't find a localized version matching exactly it MUST try to substitute it.
+    # Substitution MUST always return more specific matches for general queries.
+    # e.g. if "it" is requested and the server has "it-CH" available it returns this string.
+    # 
+    # Substitution SHOULD NOT cross language barriers, e.g. returning "en-GB" for a string requested
+    # in "cy-GB". Substitution MUST NOT return a localization in a different language unless server
+    # has a priori knowledge that the user can read and understand said language.
+    #
+    # Substitution SHOULD prefer unspecified subtags over wrong subtags. If "es-AR" is requested and a
+    # server has "es", and "es-VE" available, "es" should be selected.
+    # 
+    # A server MUST set the output `lang` field to the exact tag that the content it sends was written
+    # in and `content` to the localized string. 
+    # E.g. If a string is requested for "sr" and the server has found a string that was configured as
+    # "sr-Cyrl-BA" the server sets lang to "sr-Cyrl-BA".
+    #
+    # If a server can't find a suitable substitute it MUST set the output `content` to a NULL pointer
+    # and set the output `lang` to the input `lang` it was passed.
     # If a server can't parse a given `lang` tag it MUST set the output `lang` to a NULL pointer.
 
     available @1 () -> ( langs :List(Text) );