Update precondition

Author: ivopintodasilva

FlexibleDiff.xcodeproj/project.xcworkspace/xcshareddata/IDEWorkspaceChecks.plist

@@ -0,0 +1,8 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
+<plist version="1.0">
+<dict>
+	<key>IDEDidComputeMac32BitWarning</key>
+	<true/>
+</dict>
+</plist>

FlexibleDiff/SectionedChangeset.swift

@@ -29,8 +29,8 @@ public struct SectionedChangeset {
 	/// The changes of sections.
 	///
 	/// - precondition: Offsets in `sections.mutations` and `sections.moves` must have a
-	///                 corresponding entry in `mutatedSections` if they represent a
-	///                 mutation.
+	///                 corresponding entry in `mutatedSections` if their metadata has
+	///                 been mutated.
 	public var sections = Changeset()
 
 	/// The changes of items in the mutated sections.