docs: add Span to documentation

docs/Summary.md

@@ -45,6 +45,7 @@
   - [PointRef](api/locations/point-ref.md)
   - [Range](api/locations/range.md)
   - [RangeRef](api/locations/range-ref.md)
+  - [Span](api/locations/span.md)
 - [Operation](api/operation.md)
 
 ## Libraries

docs/api/locations/README.md

@@ -11,3 +11,4 @@ type Location = Path | Point | Range
 - [Point](./point.md)
 - [PointEntry](./pointe-entry.md)
 - [Range](./range.md)
+- [Span](./span.md)

docs/api/locations/span.md

@@ -0,0 +1,18 @@
+# Span
+
+A `Span` is a low-level way to refer to a range using `Element` as the end points instead of a `Point` which requires the use of leaf text nodes.
+
+```typescript
+type Span = [Path, Path]
+```
+
+- [Static methods](range.md#static-methods)
+  - [Check methods](range.md#check-methods)
+
+## Static Methods
+
+### Check Methods
+
+#### `Span.isSpan(value: any) => value is Span`
+
+Check if a `value` implements the `Span` interface.