Visible tabs demo #include "syscalls.h" /* getchar: simple buffered version */ int getchar(void) { static char buf[BUFSIZ]; static char *bufp = buf; static int n = 0; if (n == 0) { /* buffer is empty */ n = read(0, buf, sizeof buf); bufp = buf; } return (--n >= 0) ? (unsigned char) *bufp++ : EOF; } Tabs inside the editor are spans with the class cm-tab, and can be styled.