diff --git a/docs/specs/spec-meta-deposit.rst b/docs/specs/spec-meta-deposit.rst
index d6726b99..6ef3c30a 100644
--- a/docs/specs/spec-meta-deposit.rst
+++ b/docs/specs/spec-meta-deposit.rst
@@ -1,106 +1,118 @@
 The metadata-deposit
 ====================
 
 Goal
 ----
 A client wishes to deposit only metadata about an origin or object in the
 Software Heritage archive.
 
 The metadata-deposit is a special deposit where no content is
 provided and the data transferred to Software Heritage is only
 the metadata about an object in the archive.
 
 Requirements
 ------------
 The scope of the metadata-deposit is different than the
 sparse-deposit. While a sparse-deposit creates a revision with referenced
 directories and content files, the metadata-deposit references any of the
 following:
 
 - origin
 - snapshot
 - release
 - revision
 - directory
 - content
 
 
 A complete metadata example
 ---------------------------
 The reference element is included in the metadata xml atomEntry under the
 swh namespace:
 
 TODO: publish schema at https://www.softwareheritage.org/schema/2018/deposit
 
 .. code:: xml
 
   <?xml version="1.0"?>
   <entry xmlns="http://www.w3.org/2005/Atom"
            xmlns:codemeta="https://doi.org/10.5063/SCHEMA/CODEMETA-2.0"
            xmlns:swh="https://www.softwareheritage.org/schema/2018/deposit">
       <author>
         <name>HAL</name>
         <email>hal@ccsd.cnrs.fr</email>
       </author>
       <client>hal</client>
       <external_identifier>hal-01243573</external_identifier>
       <codemeta:name>The assignment problem</codemeta:name>
       <codemeta:url>https://hal.archives-ouvertes.fr/hal-01243573</codemeta:url>
       <codemeta:identifier>other identifier, DOI, ARK</codemeta:identifier>
       <codemeta:applicationCategory>Domain</codemeta:applicationCategory>
       <codemeta:description>description</codemeta:description>
       <codemeta:author>
         <codemeta:name> author1 </codemeta:name>
         <codemeta:affiliation> Inria </codemeta:affiliation>
         <codemeta:affiliation> UPMC </codemeta:affiliation>
       </codemeta:author>
       <codemeta:author>
         <codemeta:name> author2 </codemeta:name>
         <codemeta:affiliation> Inria </codemeta:affiliation>
         <codemeta:affiliation> UPMC </codemeta:affiliation>
       </codemeta:author>
       <swh:deposit>
         <swh:reference>
           <swh:origin url='https://github.com/user/repo'/>
         </swh:reference>
       </swh:deposit>
   </entry>
 
 References
 ^^^^^^^^^^
 
 Origins
 =======
 
 The metadata may be on an origin, identified by the origin's URL:
 
 .. code:: xml
 
   <swh:deposit>
     <swh:reference>
       <swh:origin url="https://github.com/user/repo" />
     </swh:reference>
   </swh:deposit>
 
 Graph objects
 =============
 
 It may also reference an object in the `SWH graph <data-model>`: contents,
 directories, revisions, releases, and snapshots:
 
 .. code:: xml
 
   <swh:deposit>
     <swh:reference>
       <swh:object swhid="swh:1:xxx:aaaaaaaaaaaaaa..." />
     </swh:reference>
   </swh:deposit>
 
+The value of the ``swhid`` attribute must be a `SWHID <persistent-identifiers>`,
+with any context qualifiers in this list:
+
+* ``origin``
+* ``visit``
+* ``anchor``
+* ``path``
+
+and they should be provided whenever relevant, especially ``origin``.
+
+Other qualifiers are not allowed (for example, ``line`` isn't because SWH
+cannot store metadata at a finer level than entire contents).
 
 
 Loading procedure
 ------------------
 
 In this case, the metadata-deposit will be injected as a metadata entry of
 the relevant object, with the information about the contributor of the deposit.
 Contrary to the complete and sparse deposit, there will be no object creation.