[ Todo ] When XHP version 4 is released, update the docs about runtime validation in user-documentation.

[lexidor]

Let's wait until <xhp:4/> to update :xhp:$ENABLE_VALIDATION.

Originally posted by @lexidor in hhvm/user-documentation#824 (comment)

[fredemmott]

This should just be done; any changes to make the README accurate for this branch are greatly appreciated :)

If this ends up being misleading, I'll switch the default branch for the repo so github shows 3.x by default

[lexidor]

This is referring to the docs on hacklang.org. There we still show the legacy way of disabling xhp validation. This has not been true in xhp 3 and 4, but xhp 3 has support for both attribute and child validation, while xhp 4 only validates children.