ne's manual

4.11.1: InsertChar

cursor position. code has always to be different from 0. All the currently active options (insert, word wrapping, auto indent, et cetera) are applied.

Note that inserting a line feed (10) is completely different from inserting a line with InsertLine. InsertChar 10 puts the control char CONTROL-J in the text at the current cursor position. See InsertLine.