Get form data select input and add it to page frontmatter

Support Forms & Blueprints
2

So I have gotten a bit further… I have no idea how I got this far, how did $result = $form->value()->toArray(); know I wanted to get the selected option from this form?:

-
    name: taxonomy
    type: select
    size: long
    classes: fancy
    label: Category
    options:
        project: Project
        value2: Test
        value3: test2

From Add page to from PHP

$result = $form->value()->toArray();
$page_frontmatter['taxonomy'] = $result;

which becomes in frontmatter

taxonomy: project

and I try to make it like this:

taxonomy:
    category:
        - Projects