Problem with setting default argument in Typo3 routeEnhancer - yaml

Question

I have a Typo3 page that works with two URL parameters, "manuscript" and "type" (e.g. localhost/my-page?manuscript=samplemanuscript&type=description). "manuscript" is a mandatory parameter, while "type" is optional.
I use Route Enhancers to get rid of cHash in the URL. So I have created a yaml file to configure it.
This configuration works fine without "defaults" section with both parameters in place, but when I add the defaults section to make "type" parameter optional, the URL localhost/my-page/samplemanuscript works fine, but localhost/my-page/samplemanuscript/description shows me the 404 error. Any ideas what's wrong with it?
I use Typo3 v10.4
routeEnhancers:
ManuscriptHierarchy:
type: Simple
limitToPages: [13]
routePath: '/{manuscript}/{type}'
defaults:
type: ''
aspects:
manuscript:
type: StaticValueMapper
map:
samplemanuscript: samplemanuscript
samplemanuscript2: samplemanuscript2
type:
type: StaticValueMapper
map:
transcription: transcription
description: description
P.S.
For debugging purposes, is there any appropriate way to check the final resolved URL (when I visit localhost/my-page/samplemanuscript/description)?

Answer 1

The solution looks strange to me but it works by adding requirements:
routeEnhancers:
ManuscriptHierarchy:
type: Simple
limitToPages: [13]
routePath: '/{manuscript}/{type}'
defaults:
type: ''
requirements:
manuscript: '^(?:samplemanuscript|samplemanuscript2)$'
type: '^(?:description|transcription)$'
aspects:
manuscript:
type: StaticValueMapper
map:
samplemanuscript: samplemanuscript
samplemanuscript2: samplemanuscript2
type:
type: StaticValueMapper
map:
transcription: transcription
description: description