Hello, I've created a YAML file where the value 6000_5000 was stored. This YAML was simply created for populating database tables with data for test cases. When I wrote the test case, I searched for data containing 6000_5000 but had no results. After some research, I saw, that 6000_5000 was saved as 60005000, so I digged deep to see why that happens.

I found this line (including blame) and this PR where it states

Allows to use the _ to group "big" ints, as suggested in the yaml integer type specification. As discussed in #18094, we should check if it is still part of the 1.2 specification, but I don't really see why not?

Okay, so I searched a bit and found this type definition where it states exactly what the PR should do, however this is, as the PR, for YAML version 1.1, so I opened the int specs for 1.2 which you can find here

In this definition, there is no mentioning of using _ as readability help, and I didn't find this recommendation anywhere else, so in order to comply with 1.2 standards of the YAML definition, I'd say Symfony needs to remove this.

Now I don't know how to handle this correctly. I'd open a PR, but this is a BC break, so it's not possible to merge this into the 4.x branch, but this violates the YAML definition, so a user, who reads version 1.2 of the YAML definition and uses Symfony will have NO idea WHY this happens.

Thoughts?