diff --git a/src/mol-data/int/ordered-set.ts b/src/mol-data/int/ordered-set.ts
index 4ec45b17f185c1343a44e454c641879dbb58ae92..3b7d03d397142a93ef3286cacdf5c1b5948eb587 100644
--- a/src/mol-data/int/ordered-set.ts
+++ b/src/mol-data/int/ordered-set.ts
@@ -21,6 +21,7 @@ namespace OrderedSet {
     export const has: <T extends number = number>(set: OrderedSet<T>, x: T) => boolean = Base.has as any;
     /** Returns the index of `x` in `set` or -1 if not found. */
     export const indexOf: <T extends number = number>(set: OrderedSet<T>, x: T) => number = Base.indexOf as any;
+    /** Returns the value in `set` at index `i`. */
     export const getAt: <T extends number = number>(set: OrderedSet<T>, i: number) => T = Base.getAt as any;
 
     export const min: <T extends number = number>(set: OrderedSet<T>) => T = Base.min as any;
diff --git a/src/mol-data/int/segmentation.ts b/src/mol-data/int/segmentation.ts
index 7062733eeaf6ae039febf1767eba5b886a9018cf..8d26c5f1f67e023fbd225e9fe2e9084e741e0d50 100644
--- a/src/mol-data/int/segmentation.ts
+++ b/src/mol-data/int/segmentation.ts
@@ -18,7 +18,7 @@ namespace Segmentation {
     export const getSegment: <T extends number = number, I extends number = number>(segs: Segmentation<T, I>, value: T) => number = Impl.getSegment as any;
     export const projectValue: <T extends number = number, I extends number = number>(segs: Segmentation<T, I>, set: OrderedSet<T>, value: T) => Interval = Impl.projectValue as any;
 
-    // Segment iterator that mutates a single segment object to mark all the segments.
+    /** Segment iterator that mutates a single segment object to mark all the segments. */
     export const transientSegments: <T extends number = number, I extends number = number>(segs: Segmentation<T, I>, set: OrderedSet<T>, segment?: Segment) => Impl.SegmentIterator<I> = Impl.segments as any;
 
     export type SegmentIterator<I extends number = number> = Impl.SegmentIterator<I>
diff --git a/src/mol-model/structure/export/categories/modified-residues.ts b/src/mol-model/structure/export/categories/modified-residues.ts
index 2e9183f88784900b765cde496a00a8255d7df7a3..39eb324f85c6834fde2c6f01c8b11907abeca371 100644
--- a/src/mol-model/structure/export/categories/modified-residues.ts
+++ b/src/mol-model/structure/export/categories/modified-residues.ts
@@ -28,7 +28,7 @@ const pdbx_struct_mod_residue_fields: CifField<number, StructureElement[]>[] = [
 ];
 
 function getModifiedResidues({ structures }: CifExportContext): StructureElement[] {
-    // TODO: can different models have differnt modified residues?
+    // TODO: can different models (in the same mmCIF file) have different modified residues?
     const structure = structures[0], model = structure.model;
     const map = model.properties.modifiedResidues.parentId;
     if (!map.size) return [];