Add some comments to new API in wasm.ts (#4712)

Signed-off-by: Nick Cameron <nrc@ncameron.org>

src/lang/wasm.ts

@@ -93,12 +93,26 @@ export type { Solid } from '../wasm-lib/kcl/bindings/Solid'
 export type { KclValue } from '../wasm-lib/kcl/bindings/KclValue'
 export type { ExtrudeSurface } from '../wasm-lib/kcl/bindings/ExtrudeSurface'
 
+/**
+ * The first two items are the start and end points (byte offsets from the start of the file).
+ * The third item is whether the source range belongs to the 'main' file, i.e., the file currently
+ * being rendered/displayed in the editor (TODO we need to handle modules better in the frontend).
+ */
 export type SourceRange = [number, number, boolean]
 
+/**
+ * Convert a SourceRange as used inside the KCL interpreter into the above one for use in the
+ * frontend (essentially we're eagerly checking whether the frontend should care about the SourceRange
+ * so as not to expose details of the interpreter's current representation of module ids throughout
+ * the frontend).
+ */
 export function sourceRangeFromRust(s: RustSourceRange): SourceRange {
   return [s[0], s[1], s[2] === 0]
 }
 
+/**
+ * Create a default SourceRange for testing or as a placeholder.
+ */
 export function defaultSourceRange(): SourceRange {
   return [0, 0, true]
 }
@@ -164,6 +178,10 @@ export class ParseResult {
   }
 }
 
+/**
+ * Parsing was successful. There is guaranteed to be an AST and no fatal errors. There may or may
+ * not be warnings or non-fatal errors.
+ */
 class SuccessParseResult extends ParseResult {
   program: Node<Program>