[dev] CustomerTicketZoom customisation

Hi, New to OTRS and currently trying to "improve"/customise some of the different frontend aspects. In Kernel/Output/HTML/Standard/CustomerTicketZoom.dtl, I wonder why the current ticket last subject is not displayed by default ? (is it a bug) ? I would like to display it by default and add a disabled tag to the HTML line around line 133 so Customers can't change the ticket subject, only agents can do that. to not a problem for disabled : it works well but can't understand why $QData{"Subject"} is currently empty ? By the way, how does blocks with <!-- dtl:block:xxxx --> works ? Can't understand what is their utility ? Thanks for your answer. Laurent