submodules/rlp/puzzles/html/tracks.html

Tracks
<p>
Complete the track from A to B so that the rows and
columns contain the same number of track segments as are indicated in the
clues to the top and right of the grid. There are only straight and
90-degree curved rail sections, and the track may not cross itself.
<p>
Left-click on an edge between two squares to add a track segment between
the two squares. Right-click on an edge to add a cross on the edge,
indicating no track is possible there.
<p>
Left-click in a square to add a colour indicator showing that you know the
square must contain a track, even if you don't know which edges it crosses
yet. Right-click in a square to add a cross indicating it contains no
track segment.
<p>
Left- or right-drag between squares to lay a straight line of is-track or
is-not-track indicators, useful for filling in rows or columns to match the
clue.