The minimum distance at which two text fragments will be assumed
to be part of one undivided word. This value is specified in terms
of a fraction of the font size.
PDF text does not always include spaces. It is not uncommon for
spaces simply to be indicated by the positions at which characters
are drawn. The fact that two text fragments are drawn some distance
from each other visually indicates that there is a space between
them. When extracting text from a PDF one needs to decide how far
apart text fragments can be, before one assumes that they should be
separated by a space.
This property allows you to control this spacing. Increasing the
property will tend to reduce the cohesiveness of fragments
resulting in fewer spaces. Decreasing it will tend to increase the
cohesiveness resulting in more spaces.
Broadly speaking the property is defined as the proportion of
the font size at which distance a space will be assumed to be
present. The precise mechanism is a little more complicated than
this as it needs to take account of vertical distance and of
varying font sizes between fragments. However for most purposes the
broad definition will be acceptable.