Hi team,

As discussed in #25806, there is a small breaking change between 4.0 to 4.1 in that users can no longer use .collapse.show classes to indicate that an element should be displayed. The new behaviour is that .collapse:not(.show) elements should be hidden, which is a slightly different behaviour.

It would be great it we could note this somewhere in the migration guide: https://github.com/twbs/bootstrap/blob/v4-dev/site/docs/4.1/migration.md