we display the median spectra for the full sample and the low/high-stretch subsamples. We also display the best-fitting double-Gaussian fits (after removing a linear pseudo-continuum) to each line profile. For each case, we performed a six–parameter fit, allowing the centroid, width, and height of each Gaussian to vary. The centroid of each Gaussian corresponds roughly to the characteristic velocity of that component. Similarly, the width of each feature corresponds to the velocity-width of the absorbing region for that feature. Finally, the height of each feature is roughly related to the amount of absorbing material at a given velocity. The six–parameter double-Gaussian fits to each profile are represented by the blue lines in Figure \[f:dgauss\].

We also fit the low/high-stretch subsamples with two parameters fixed and four allowed to vary. The centroid and width (the parameters related to velocity) of the redder Gaussian was fixed to match the best-fitting values for the full-sample median spectrum, and the remaining parameters (all parameters for the bluer Gaussian and the height of the redder Gaussian) were allowed to vary. These fits are represented by the red lines in Figure \[f:dgauss\]. Visually, the six–parameter fit is not a significantly better representation of the data than 