The XY file gives all of the information about the spectrum. It is contained in five columns:

  wavelength  flux  error_in_flux(1sigma) continuum  flag

The wavelength is given in units of angstroms.
The flux, error in the flux, and continuum are all given in units of 10^-16 erg cm^-2 s^-1 Å^-1
The flag indicates whether or not the pixel was used in the continuum fit.

List of lines that are greater than 3.5 sigma -- see text
An example file is given below:

0014+813 3.384  2.7428   3.384   70.   .150   .150   250.   300.    -1. 
Line Lambda   sig     EW  sig    SL   FWHM      z         Line ID    
---- ------- -----  ----- ---- ----- -----  -----------  ----------  
  1  4555.75  0.05   1.20 0.08  16.0  1.50  0.00000( 0)              
  2  4558.98  0.06   1.55 0.09  16.3  2.26  0.00000( 0)              
  3  4562.53  0.05   1.35 0.09  15.9  1.90  0.00000( 0)              ... 

The first line contains:
quasar name
quasar redshift
redshift of lyman alpha at blue end of observed spectrum
redshift of lyman alpha at red end of range -- usually = quasar redshift, but not always.
resolution of data, km/sec
rest equivalent width threshold for data at z rest equivalent width threshold for data with z(em)-0.15 < z < z(em), Angstroms
fnu(mJy): at 911 A, as extrapolated from longer wavelengths
fnu(mJy): at 1450 A, for the HST sample we will measure the observed flux at 1450 A for most objects
fnu(mJy): at 911 A, as observed directly (Galactic reddening corrected) if
available, -1. if not observed directly

The first line may be read by a formated read:
format(a8,1x,f5.3,2x,f6.4,4x,f5.3,3x,f4.0,5x,f4.3,3x,f4.3,1x, f6.1,1x,f6.1,1x,f6.1)

Each line has the start and stop wavelengths of a CHUNK of good data to be used. The chunks exclude all bad pixel regions and any identified strong metal line systems, e.g.

4555.8 4581.6
4585.4 4618.7
4618.7 4708.4
4725.0 4776.2
4780.7 4899.5
4899.5 4949.3 ...

Contains an integer, wavelength (Angstroms), 3.5-sigma threshold (Angstroms), e.g.

    1     4552.899       0.3824  
    2     4555.649       0.3472 
    3     4558.399       0.3378