track index issue : a WALTER guru is needed...

Read the bit in expression about the last four digits (Attach) That is how you attach any element to the bounds of it's container (So for the MCP for instance the MCP size itself will be the container bounds)

Sometimes you need to set really large margin offsets to make it behave otherwise as the track hight increases it will flip 90 degrees. i.e .

Still doesn't work, no matter the values used for tcp.trackidx.margins. As a workaround, I found a way to differentiate different type of tracks with these walter statements : set tcp.trackidx [0 0 29 41] set tcp.trackidx.margin [0 0 0 0 1] This way, the track index remains fixed and I use transparent tcp_idxbg(_sel).png files including different symbols according to the layouts. Not perfect, as I would have liked to get plain colors in the track index zone of each track, but I'll do with this for now, as I have wasted too much time on this already and need to test many other Reaper features. But any suggestion is still welcomed and thanks for the help already provided. :)