\setuppapersize[A8]

% Spaces are ignored at the beginning and end of a line note. Hyphenation is
% supported in all cases.

\starttext

    \startlinenumbering
        This text shows \startlinenote[a]{both spaces} variant \stoplinenote[a]. \par
        This text shows \startlinenote[b]{left space} variant\stoplinenote[b].   \par
        This text shows \startlinenote[c]{right space}variant \stoplinenote[c].  \par
        This text shows \startlinenote[d]{no spaces}variant\stoplinenote[d].     \par
    \stoplinenumbering

\stoptext

