restructured code in separated files

src/group.typ

@@ -0,0 +1,52 @@
+#import "@preview/cetz:0.2.2": draw
+
+#let _grp(name, desc: none, type: "default", elmts) = {
+  return ((
+    type: "grp",
+    name: name,
+    desc: desc,
+    grp-type: type,
+    elmts: elmts
+  ),)
+}
+
+#let render(x0, x1, y0, y1, group) = {
+  let shapes = ()
+  let m = measure(box(group.name))
+  let w = m.width / 1pt + 15
+  let h = m.height / 1pt + 6
+  shapes += draw.rect(
+    (x0, y0),
+    (x1, y1)
+  )
+  shapes += draw.merge-path(
+    fill: gray.lighten(20%),
+    close: true,
+    {
+      draw.line(
+        (x0, y0),
+        (x0 + w, y0),
+        (x0 + w, y0 - h / 2),
+        (x0 + w - 5, y0 - h),
+        (x0, y0 - h)
+      )
+    }
+  )
+  shapes += draw.content(
+    (x0, y0),
+    group.name,
+    anchor: "north-west",
+    padding: (left: 5pt, right: 10pt, top: 3pt, bottom: 3pt)
+  )
+
+  if group.desc != none {
+    shapes += draw.content(
+      (x0 + w, y0),
+      text([\[#group.desc\]], weight: "bold"),
+      anchor: "north-west",
+      padding: 3pt
+    )
+  }
+
+  return shapes
+}