diff --git a/__tests__/models.spec.ts b/__tests__/models.spec.ts
index ba0fa2d..5fcb8ec 100644
--- a/__tests__/models.spec.ts
+++ b/__tests__/models.spec.ts
@@ -156,6 +156,54 @@ describe('audios model', () => {
 	})
 })
 
+/** Register the four built-in handlers, the way each suite below does */
+async function registerAll() {
+	const [images, videos, audios, sheetmusic] = await Promise.all([
+		import('../lib/models/images.ts'),
+		import('../lib/models/videos.ts'),
+		import('../lib/models/audios.ts'),
+		import('../lib/models/sheetmusic.ts'),
+	])
+	images.registerImageHandler()
+	videos.registerVideoHandler()
+	audios.registerAudioHandler()
+	sheetmusic.registerSheetmusicHandler()
+}
+
+describe('a selection of more than one file', () => {
+	// Every handler answers for the whole selection, so one file it cannot
+	// open has to disqualify the lot. Written for all of them at once
+	// because `every` reads exactly like `some` until something asks.
+	it.each([
+		['images', 'image/jpeg', 'application/pdf'],
+		['videos', 'video/mp4', 'application/pdf'],
+		['audios', 'audio/mpeg', 'application/pdf'],
+		['sheetmusic', 'application/vnd.recordare.musicxml', 'application/pdf'],
+	])('%s refuses a selection it can only partly open', async (id, supported, other) => {
+		await registerAll()
+		const handler = handlerById(id)
+
+		expect(handler.enabled([makeFile({ mime: supported })])).toBe(true)
+		expect(handler.enabled([
+			makeFile({ mime: supported }),
+			makeFile({ mime: other }),
+		])).toBe(false)
+	})
+
+	it.each([
+		['images', 'image/jpeg', 'image/png'],
+		['audios', 'audio/mpeg', 'audio/flac'],
+	])('%s takes a selection it can open all of', async (id, first, second) => {
+		await registerAll()
+		const handler = handlerById(id)
+
+		expect(handler.enabled([
+			makeFile({ mime: first }),
+			makeFile({ mime: second }),
+		])).toBe(true)
+	})
+})
+
 describe('sheetmusic model', () => {
 	it.each([
 		'application/vnd.recordare.musicxml',
diff --git a/__tests__/scope.spec.ts b/__tests__/scope.spec.ts
index b199055..e9783da 100644
--- a/__tests__/scope.spec.ts
+++ b/__tests__/scope.spec.ts
@@ -20,6 +20,31 @@ describe('compareVersions', () => {
 
 	it('ranks a release above its own prereleases', () => {
 		expect(compareVersions('2.0.0', '2.0.0-beta.1')).toBeGreaterThan(0)
+		// Both ways round. Only one direction was asserted, and the election
+		// asks in whichever order the two copies happen to load, so a beta
+		// could have won a page against a release with nothing to show for it
+		expect(compareVersions('2.0.0-beta.1', '2.0.0')).toBeLessThan(0)
+	})
+
+	it('is the same comparison whichever way it is asked', () => {
+		// Adding zero, because Math.sign(0) is 0 and negating it is -0, and
+		// the two are not the same value to a strict comparison
+		const sign = (value: number) => Math.sign(value) + 0
+		const versions = ['1.9.9', '2.0.0-1', '2.0.0-alpha', '2.0.0-beta.2', '2.0.0-beta.10', '2.0.0', '2.0.1']
+		for (const a of versions) {
+			for (const b of versions) {
+				expect(sign(compareVersions(a, b)), `${a} against ${b}`)
+					.toBe(-sign(compareVersions(b, a)) + 0)
+			}
+		}
+	})
+
+	it('orders a full run of versions the way semver does', () => {
+		// Sorting the list is the question the election actually asks
+		const ordered = ['1.9.9', '2.0.0-1', '2.0.0-alpha', '2.0.0-beta.2', '2.0.0-beta.10', '2.0.0', '2.0.1']
+		const shuffled = ['2.0.0', '2.0.0-beta.10', '1.9.9', '2.0.1', '2.0.0-alpha', '2.0.0-1', '2.0.0-beta.2']
+
+		expect([...shuffled].sort(compareVersions)).toEqual(ordered)
 	})
 
 	it('compares prerelease identifiers the way semver does', () => {
diff --git a/stryker.config.json b/stryker.config.json
index c0b700f..d3c5468 100644
--- a/stryker.config.json
+++ b/stryker.config.json
@@ -1,6 +1,6 @@
 {
 	"$schema": "./node_modules/@stryker-mutator/core/schema/stryker-schema.json",
-	"_comment": "Audits the tests rather than the code: every mutant that survives is a change to the library that no test noticed. Scoped to the pure logic, where it is fast and where a surviving mutant almost always means a real gap rather than an equivalent one.",
+	"_comment": "Audits the tests rather than the code: a mutant that survives is a change no test noticed. Scoped to the logic, where a survivor usually means a real gap. Components and views are left out: most of their mutants are DOM glue that a unit test cannot observe, so the score would measure the wrong thing.",
 	"packageManager": "npm",
 	"testRunner": "vitest",
 	"inPlace": true,
@@ -17,10 +17,15 @@
 	},
 	"coverageAnalysis": "perTest",
 	"mutate": [
+		"lib/*.ts",
 		"lib/utils/**/*.ts",
 		"lib/composables/**/*.ts",
+		"lib/models/**/*.ts",
+		"lib/services/**/*.ts",
+		"lib/helpers/**/*.ts",
 		"!lib/**/*.d.ts",
-		"!lib/utils/plyrTranslations.ts"
+		"!lib/utils/plyrTranslations.ts",
+		"!lib/services/logger.ts"
 	],
 	"thresholds": {
 		"high": 90,