Improve the comments in the assembly module

Also, remove trailing comma.

app-proto/src/assembly.rs

@@ -30,8 +30,11 @@ pub struct Element {
     pub label: String,
     pub color: ElementColor,
     pub representation: Signal<DVector<f64>>,
+    
+    // the regulators that affect this element. the ambient assembly is
+    // responsible for keeping this set up to date
     pub regulators: Signal<BTreeSet<RegulatorKey>>,
-
+    
     // a serial number, assigned by `Element::new`, that uniquely identifies
     // each element
     pub serial: u64,
@@ -117,7 +120,7 @@ impl Element {
 
 // to construct a `SpecifiedValue` that might be `Present`, use the associated
 // function `try_from`. this ensures that `spec` is always a valid specification
-// of `value` according to the format discussed above the implementation of
+// of `value` according to the format discussed at the implementation of
 // `TryFrom<String>`
 pub enum SpecifiedValue {
     Absent,
@@ -154,7 +157,8 @@ impl SpecifiedValue {
 // specification is empty, the `SpecifiedValue` is `Absent`. if the
 // specification parses to a floating-point value `x`, the `SpecifiedValue` is
 // `Present`, with a `value` of `x`, and the specification is stored in `spec`.
-// these are the only valid specifications; any other produces an error
+// these are currently the only valid specifications; any other produces an
+// error
 impl TryFrom<String> for SpecifiedValue {
     type Error = ParseFloatError;
     
@@ -183,7 +187,7 @@ impl Regulator {
                 self.set_point.set(set_pt);
                 true
             }
-            Err(_) => false,
+            Err(_) => false
         }
     }
 }
@@ -272,7 +276,7 @@ impl Assembly {
         );
     }
     
-    pub fn insert_regulator(&self, regulator: Regulator) {
+    fn insert_regulator(&self, regulator: Regulator) {
         let subjects = regulator.subjects;
         let key = self.regulators.update(|regs| regs.insert(regulator));
         let subject_regulators = self.elements.with(