In current datebox, if the user type a date that doesn't exist in the real calendar, it will automatically be calculated based on the closest existing date.
for example:
Jan 0 2018 = (Jan 1 2018) - (1day) = Dec 31 2017
Jan 32 2018 = (Jan 31 2018) + (1day) = Feb 1 2018

If a developper want to prevent this calculation, a partial solution is to use lenient=false on the datebox.
However, this is not perfect, since lenient false will also prevent the datebox from trying to parse non-perfect template inputs

New feature:
Add a new attribute to the datebox to decide to allow for this calculation or not, not affected by lenient mode.
for example:
<datebox lenient="true" strictDate="true"/>
would allow imperfect patterns, but block date calculation.

<datebox lenient="false" strictDate="false"/>
would only accept valid date patterns, but also allow calculation if the result is not a real world date. (0 Jan > 31 Dec, 32 Jan > 1 Feb, etc)

Current calculation:
https://github.com/zkoss/zk/blob/master/zul/src/archive/web/js/zul/db/datefmt.js#L394