%N window
The use of "select=window" is used to select a subset of spectral
 windows (or IF bands in AIPS terminology) in a uv data-set. For
 example, to select the second and third spectral windows, use

   select=window(2,3)

 Some explanation is needed for the interaction between "select=window"
 and the line keyword.

 Window selection complements velocity linetypes (line=velocity or
 line=felocity). In this case only data from the selected windows
 is used in determining the velocity channels.

 There are some limitations when using window selection with channel
 linetype ("line=channel"). Firstly the selected windows must
 be contiguous (i.e. you cannot give "select=window(1,4)") when combined
 with "line=channel" selection. Secondly the channel specification
 in the line keyword is relative to the first channel in the first
 selected window. For example, if you use

   line=channel,10,1,1 select=window(2,3)

 you will be get 10 channels starting from the first channel in window
 2. If windows 2 and 3 had 8 channels each, then you would get all
 8 channels from window 2, and the first two channels from window 3.
