[Issue] resolved consistency error for merged indexer xml files

[m2-assistant]

This issue is automatically created based on existing pull request: #27212: resolved consistency error for merged indexer xml files

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The allowed values in classType should be equal in unmerged and merged indexer.xml files

Allowing only letters and backspaces is wrong, since PHP-namespaces can also contain numbers.

Preconditions: (*)

Magento 2.4-develop

Related Pull Requests

Fixed Issues (if relevant)

1. magento/magento2#<issue_number>: Issue title

Steps to Reproduce: (*)

1. Create a simple module with a vendor name which contains at least one number (ex. Cus2tom2)
2. Add a custom indexer to the module just like on the devdocs
3. Run in console: php bin/magento setup:upgrade;

Actual Result: ✖️ Invalid doc element "indexer" , attribute "class" ...

Expected Result: ✔️ Normal Upgrade output & module gets properly installed.

Questions or comments

Contribution checklist (*)

• Pull request has a meaningful description of its purpose
• All commits are accompanied by meaningful commit messages
• All new or changed code is covered with unit/integration tests (if applicable)
• All automated tests passed successfully (all builds are green)