Update advanced-examples.md

docs/advanced-examples.md

@@ -5,3 +5,20 @@ In this section of the docs you will find some advanced usage examples of modal-
 ## Nesting form calls
 
 ## Modifying frontmatter with a form
+
+If you want to modify the content of a notes frontmatter with one of your existing forms, put the following
+snippet in a templater template, substituting the name of your form:
+
+```js
+<%*
+const modalForm = app.plugins.plugins.modalforms.api; 
+app.fileManager.processFrontMatter(tp.config.target_file,
+  async (frontmatter) => { 
+      const result = await modalForm.openForm('example-form', { values: {...frontmatter}});
+      Object.assign(frontmatter, result.getData()); 
+  })}, 200)
+%>
+```
+
+The values the form understand and that are pressent in the frontmatter, will be populated with the values on the frontmatter.
+Then, when you submit the form, the new values will overwrite the old ones, leaving the rest untouched.