No, ~abc will be interpreted as the home directory of user abc in Tcl 8.*

Then you fix this mistake, not remove ~ completely

It's not a mistake

If it's not a mistake then why they took it off?

The original design decision was to behave like a shell, where ~ means your own home dir and ~fred means fred's home dir. With the benefit of experience, this is now seen to be unwise and a different decision has been made.

So they copied the mistake from some shell (you don't need much experience to realize it's unwise not to use a separator to separate)