\input luaotfload.sty
%% lookup font by name (involving database)
\font\first=name:iwonaregular at 42pt
%% lookup font by file name (kpse)
\font\second=file:antpoltltsemiexpd-bolditalic.otf at 42pt
%% lookup font by name, with style in slash notation
\font\third={name:Antykwa torunska/I} at 42pt
%% unspecified lookup; in definers.read:
%%  - first it falls back to “file”
%%  - empty “method” field triggers fallback to “name”
%%  - names.resolve -> kpse.lookup -> hit!
\font\fourth=iwona at 42pt

{\first   foo \endgraf}
{\second  bar \endgraf}
{\third   baz \endgraf}
{\fourth  xyzzy \endgraf}

\bye

