  Many models for coronal loops have difficulty explaining the observed EUV
brightness of the transition region, which is often significantly less than
theoretical models predict. This discrepancy has been addressed by a variety of
approaches including filling factors and time-dependent heating. Here we focus
on an effect that has been ignored so far: the absorption of EUV light with
wavelengths below 912 {\AA} by the resonance continua of neutral hydrogen and
helium. Such absorption is expected to occur in the low-lying transition region
of hot, active region loops, that is co-located with cool chromospheric
features and called ``moss'' as a result of the reticulated appearance
resulting from the absorption. We use co-temporal and co-spatial
spectroheliograms obtained with SOHO/SUMER and Hinode/EIS of Fe XII 1242 {\AA},
195 {\AA} and 186.88 {\AA}, and compare the density determination from the
186/195 {\AA} line ratio to that resulting from the 195/1242 {\AA} line ratio.
We find significant absorption of 195 {\AA} emission caused by the
chromospheric inclusions in the moss. We find that the amount of absorption is
generally of order a factor of 2. We compare to numerical models and show that
the observed effect is well reproduced by 3D radiative MHD models of the
transition region and corona. We use STEREO A/B data of the same active region
and find that increased angles between line-of-sight and local vertical cause
additional absorption. Our determination of the amount of chromospheric
absorption of TR emission can be used to better constrain coronal heating
models.
