Выражение встречается в следующем контексте:

The Boxed Value, used at the European pre-standard (ENV) stage together with the National Application Documents, offered a National choice for a value.
It has to disappear in the EN Eurocodes.
Originally, the Eurocodes were elaborated by European Standardisation
Organisation as 62 pre-standards (ENVs). Most
were published between 1992 and 1998, but, due to difficulties in
harmonizing all the aspects of the calculation methods, the ENV Eurocodes
included "boxed values" which allowed Members States to chose other values
for use on their territory.

Заранее спасибо