Property validations

[zregvart]

For some properties we should perform validations, simple enough properties should conform to their data types by syntax (numbers should be given as digits), other properties might have slightly more elaborate rules (usernames can't contain :).

[stale[bot]]

This issue has been automatically marked as stale because it has not had any activity since 90 days. It will be closed if no further activity occurs within 7 days. Thank you for your contributions!

[zregvart]

I think we should do this.

[stale[bot]]

This issue has been automatically marked as stale because it has not had any activity since 90 days. It will be closed if no further activity occurs within 7 days. Thank you for your contributions!