The DER Finder at the expressed regions-level is done with the regionMatrix or railMatrix functions depending on the input data.
Details about both approaches are further described in the vignettes.
The DER Finder approach can also be used to identify differentially bounded ChIP-seq regions (peaks). In particular, analyzeChr has parameters that allow smoothing of the F-statistics which can be useful for anlayzing ChIP-seq data. This use case is further explained in the users guide vignette.
Frazee, A. C., Sabunciyan, S., Hansen, K. D., Irizarry, R. A. & Leek, J. T. Differential expression analysis of RNA-seq data at single-base resolution. Biostatistics (2014). doi:10.1093/biostatistics/kxt053
Rafael A. Irizarry, Martin Aryee, Hector Corrada Bravo, Kasper D. Hansen and Harris A. Jaffee. bumphunter: Bump Hunter. R package version 1.1.10.