[NTG-context] definefontfamily use

Hello, Previously, in order to make punctual use of a true-type font in a title for example, I did the following: \definefontfamily [myfont] [serif] [myfont] where myfont.ttf is located in the current project directory, and selecting the font was simply {\switchtobodyfont[myfont]My Font!} Using the present context, this yields the error selectfont > The requested font 'myfont' has no files for the 'tf' alternative, Latin Modern is used instead. What has changed and what should be the proper use? (I have tried setting explicitly [tf=file:myfont.ttf], which was only a guess.) Alan