detail not exported properties because of no support in target filetype

so when a user exports a Calc file or more precisely saves a Calc file as an 
Excel file for example, the application should show the user WHAT EXACTLY is 
causing compatibility problems.

In order to achieve such functionality, each Calc element could contain a 
flag "ExcelCompatible" for example; and then those elements where 
that flag attribute is 0 are shown to the user; perhaps with further 
info on how to avoid these incompatibilities.

Note: the flag is not stored in each instant of the element but 
static like: you keep a database (compatibility table) where you look 
up for each element that is used in the current file what the 
compatibility state is for the selected file format.

There should be such properties or else Calc could not do more than Excel, 
which means Calc is not needed which means ... ! and the user should be well 
informed when he wants to save sth he did which can't be saved.

see also issue 6494 and issue 7258