>>> [!note] Migrated issue <!-- Drupal.org comment --> <!-- Migrated from issue #3582230. --> Reported by: [jurgenhaas](https://www.drupal.org/user/168924) Related to !23 >>> <h3 id="summary-problem-motivation">Problem/Motivation</h3> <p>Some model owners have specific constraints, e.g. exactly 1 source component, or no multiple edges between nodes.</p> <p>Provide an API for such constraints that can be declared by the model owner and will be validated by the modeler.</p> <h4 id="summary-steps-reproduce">Steps to reproduce</h4> <h3 id="summary-proposed-resolution">Proposed resolution</h3> <h3 id="summary-remaining-tasks">Remaining tasks</h3> <h3 id="summary-ui-changes">User interface changes</h3> <h3 id="summary-api-changes">API changes</h3> <h3 id="summary-data-model-changes">Data model changes</h3>