set label at 0,0 "Plot origin" hypertext point pt 1
     plot 'data' using 1:2:0 with labels hypertext point pt 7 \
          title 'mouse over point to see its order in data set'
For the wxt and qt terminals, left-click on a hypertext anchor after the text has appeared will copy the hypertext to the clipboard.
EXPERIMENTAL (implementation details may change)
Text of the form "image{xsize
,
ysize
}:
filename
{
n
caption text
}" will
trigger display of the image file in a pop-up box. The optional size overrides
a default box size 300x200.  The types of image file recognized may vary by
terminal type, but *.png should always work. Any additional text lines
following the image filename are displayed as usual for hypertext.
Example:
     set label 7 "image:../figures/Fig7_inset.png\nFigure 7 caption..."
     set label 7 at 10,100 hypertext point pt 7