  Type I gamma-ray bursts (GRBs) are believed to originate from compact binary
merger usually with duration less than 2 seconds for the main emission.
However, recent observations of GRB 211211A and GRB 230307A indicate that some
merger-origin GRBs could last much longer. Since they show strikingly similar
properties (indicating a common mechanism) which are different from the classic
"long"-short burst (e.g. GRB 060614), forming an interesting subclass of type I
GRBs, we suggest to name them as type IL GRBs. By identifying the first peak of
GRB 230307A as a quasi-thermal precursor, we find that the prompt emission of
type IL GRB is composed of three episodes: (1) a precursor followed by a short
quiescent (or weak emission) period, (2) a long-duration main emission, and (3)
an extended emission. With this burst pattern, a good candidate, GRB 170228A,
was found in the Fermi/GBM archive data, and subsequent temporal and spectral
analyses indeed show that GRB 170228A falls in the same cluster with GRB
211211A and GRB 230307A in many diagnostic figures. Thus this burst pattern
could be a good reference for rapidly identifying type IL GRB and conducting
low-latency follow-up observation. We estimated the occurrence rate and
discussed the physical origins and implications for the three emission episodes
of type IL GRBs. Our analysis suggests the pre-merger precursor model,
especially the super flare model, is more favored for type IL GRBs.
