Plain text here means columns lined up with spaces, the way a command line tool prints a table.
Who uses it
Terminal output, log files, fixed-width exports from older systems.
Reading Plain Text
Two shapes are handled. If the same character positions are blank on every line, those gutters are treated as column boundaries, so values containing single spaces stay intact. Otherwise the lines are split on runs of whitespace.
Writing Plain Text
Columns are padded to the widest value. Width is counted in display columns rather than characters, so a table containing Chinese, Japanese or Korean text still lines up: those glyphs occupy two columns in a monospace font.