What is peptide isoform and how will it affect the MSGF+ search results?

[yonghanyu]

Describe the question or problem

Hi there, I saw that MSGF+ will consider 128 peptide isoforms in default. However, I’ve only heard about protein isoforms. What is peptide isoforms in MSGF+ and how will this affect the search result when using the pre-digested peptide database?

Thanks in advance!