Traditionally, the merge process attempts to merge all unresolved files
using the merge tool of choice, regardless of whether previous file merge
attempts succeeded or failed. Setting the merge.abortonfailure option to
True changes this behavior so that a failed merge will immediately abort
the merge operation, leaving the user in a normal unresolved merge state.
This is particularly useful when there may be many files to be merged and the
user just wants to abort the process by exiting their editor with an error.