PREFIX ex: <http://a.example>
PREFIX sx: <http://www.w3.org/ns/shex#>
PREFIX xsd: <http://www.w3.org/2001/XMLSchema#>

[] a sx:Schema ;
    sx:shapes (<http://a.example/S1>) .

<http://a.example/S1> a sx:ShapeDecl ; sx:shapeExpr [ a sx:Shape ;
  sx:expression [ a sx:TripleConstraint ;
    sx:predicate <http://a.example/p1>
  ];
  sx:semActs ([
    a sx:SemAct;
    sx:name <http://shex.io/extensions/Test/>
  ]) ] .