diff --git a/pyvo/registry/regtap.py b/pyvo/registry/regtap.py
index a074f1f4c..59f29fe20 100644
--- a/pyvo/registry/regtap.py
+++ b/pyvo/registry/regtap.py
@@ -122,6 +122,36 @@ def search(*constraints: rtcons.Constraint, includeaux: bool = False, maxrec: in
     *constraints : `rtcons.Constraint` instances
         The constraints (keywords to match, positions to cover, ...)
         that the returned records need to satisfy.
+        The accepted constraints are:
+
+            - keywords: one or more freetext words, mached in the title,
+              description or subject of the resource.
+            - servicetype: constrain to one of tap, ssa, sia, conesearch
+              (or full ivoids for other service types). This is the
+              constraint you want to use for service discovery.
+            - ucd: constrain by one or more UCD patterns; resources match
+              when they serve columns having a matching UCD
+              (e.g., phot.mag;em.ir.% for "any infrared magnitude").
+            - waveband: one or more terms from the vocabulary at
+              http://www.ivoa.net/rdf/messenger giving the rough spectral
+              location of the resource.
+            - author: an author ("creator"). This is a single SQL pattern,
+              and given the sloppy practices in the VO for how to write
+              author names, you should probably generously use wildcards.
+            - datamodel: one of obscore, epntap, or regtap: only return TAP
+              services having tables of this kind.
+            - ivoid: exactly match a single IVOA identifier (that is,
+              in effect, the primary key in the VO).
+            - spatial: match resources covering a certain geometry (point,
+              circle, polygon, or MOC). RegTAP 1.2 Extension.
+            - spectral: match resources covering a certain part of the spectrum
+              (usually, but not limited to, the electromagnetic spectrum).
+              RegTAP 1.2 Extension
+            - temporal: match resources covering a some point or interval in
+              time. RegTAP 1.2 Extension
+
+        Multiple constraints are combined conjunctively ("AND").
+
 
     includeaux : bool
         Flag for whether to include auxiliary capabilities in results.