diff --git a/qpms/cybspec.pyx b/qpms/cybspec.pyx
index 9983272..866c440 100644
--- a/qpms/cybspec.pyx
+++ b/qpms/cybspec.pyx
@@ -35,6 +35,13 @@ cdef class BaseSpec:
     whenever used in other wrapper classes that need the pointer
     to qpms_vswf_set_spec_t, remember to set a (private, probably immutable) reference to qpms.basespec to ensure
     correct reference counting and garbage collection.
+
+    BaseSpec can be constructed either using a single keyword argument `lMax` to include
+    all the transversal vector spherical wavefunction to a specific degree, or
+    using an explicit list of integer basis VSWF codes, \see qpms_uvswfi_t
+    BaseSpec(lMax = <positive_integer>)
+        or
+    BaseSpec([ uvswfi0, ... ])
     '''
     #cdef qpms_vswf_set_spec_t s # in pxd
     #cdef np.ndarray __ilist     # in pxd