Pressing alt-u will toggle between TSV and CSV versions of Humdrum data. The standard form of Humdrum data is in TSV format:
After pressing alt-u, the data will be displayed in CSV format:
Pressing alt-u again will revert the Humdrum data to TSV form.
The CSV form is useful for loading into software that has CSV import but not TSV import. Also, the CSV format is useful for cases where tab characters may get munged, such as in emails.
Notice that reference records (the green-colored text in the above figure) may contain tabs which are not converted into commas when converting into the CSV form. This is because such tabs are not integral to the Humdrum data structure. Tabs in global comments will also not be altered for the same reason.