Returns the first position of the given line. Lines are numbered starting with 0.
Calling this method may force the recalculation of location information if a maximum width is set for the editor, even if the editor currently has delayed refreshing (see refresh-delayed?).
To calculate lines, if the following are true:
See also paragraph-start-position, which operates on paragraphs (determined by explicit newline characters) instead of lines (determined by both explicit newline characters and automatic line-wrapping).
If there are fewer than line-1 lines, the start of the last line is returned. If line is less than 0, then the start of the first line is returned.
If the line starts with invisible items and visible? is not #f, the first position past the invisible items is returned.