The appended code is supposed to allow reduction of the inter-word spacing
in my bibliographies but it does not. Adjusting the \spaceskip in the
setups for [tightspace] does not seem to make any difference.

Any suggestions will be most welcome.

I am using the latest beta (ConTeXt  ver: 2015.11.19 19:13 MKIV beta with
LuaTeX 0.85)

Alan

\startsetups[tightspace]
  \spaceskip .7\interwordspace plus .5\interwordstretch minus
\interwordshrink
\stopsetups

\def\dostartbibitem[#1]{\startBibItem[title={#1},reference={#1}]}
\def\startbibitem{\dosingleempty\dostartbibitem}
\def\stopbibitem{\stopBibItem}

\definedescription[BibItem][
width=broad,
margin=1.5pc,
indenting={no},
indentnext=no,
alternative=hanging,
hang=1,
headcommand=\gobbleoneargument,
align=right,
before={\directsetup{tightspace}\bgroup\language[packed]},
after={\egroup},
]

\starttext

Martin, J. 1956.
\emph{Histoire du texte des phénomènes d’Aratos}. Paris.

\startbibitem[Martin 1956]
Martin, J. 1956.
\emph{Histoire du texte des phénomènes d’Aratos}. Paris.
\stopbibitem


\stoptext