The conversion process is controlled by main.format or one of it's subsidiary .format files. Template files allow a Perception author to change the appearance of the converted HTML using a series of pre-defined variables. You define which templates are used for a session from within Session Manager. Sessions either use one template file, specified in the session's control block, or separate template files for each question block, allowing for different styles to be used for different sets of questions. The whole process of converting your questions and sessions into the HTML that the browser displays is controlled within the format files.
Nothing is fixed inside that server software.
When the Perception Server software receives the instruction to display information, for example to display a set of questions, main.format defines how the HTML page is made. The structure of the HTML will contain many variables. When one is found the server software checks the specified template file. If a reference to the variables is found in the template file then it's value is used, otherwise the server software returns to the format file and uses the default value of the variable defined there. You can preview how a template file will change the appearance of a question, or question block, by using the Tryout features of either Question Manager or Session Manager.