  To better understand the ionizing properties of galaxies in the EoR, we
investigate deep, rest-frame ultraviolet (UV) spectra of $\simeq 500$
star-forming galaxies at $3 \leq z \leq 5$ selected from the public ESO-VANDELS
spectroscopic survey. The absolute ionizing photon escape fraction ($f_{\rm
esc}^{\rm abs}$) is derived by combining absorption line measurements with
estimates of the UV attenuation. The ionizing production efficiency
($\xi_{ion}$) is calculated by fitting the far-UV (FUV) stellar continuum of
the VANDELS galaxies. We find that the $f_{\rm esc}^{\rm abs}$ and $\xi_{ion}$
parameters increase towards low-mass, blue UV-continuum slopes and strong
Ly$\alpha$ emitting galaxies, and both are just slightly higher-than-average
for the UV-faintest galaxies in the sample. Potential Lyman Continuum Emitters
(LCEs) and selected Lyman Alpha Emitters (LAEs) show systematically higher
$\xi_{ion}$ ($\log \xi_{ion}$ (Hz\erg) $\approx 25.38, 25.41$) than non-LCEs
and non-LAEs ($\log \xi_{ion}$ (Hz\erg) $\approx 25.18, 25.14$) at similar UV
magnitudes. This indicates very young underlying stellar populations ($\approx
10~{\rm Myr}$) at relatively low metallicities ($\approx 0.2~{\rm Z_{\odot}}$).
The FUV non-ionizing spectra of potential LCEs is characterized by very blue UV
slopes ($\leq -2$), enhanced Ly$\alpha$ emission ($\leq -25$A), strong UV
nebular lines (e.g., high CIV1550/CIII]1908 $\geq 0.75$ ratios), and weak
absorption lines ($\leq 1$A). The latter suggests the existence of low
gas-column-density channels in the interstellar medium which enables the escape
of ionizing photons. By comparing our VANDELS results against other surveys in
the literature, our findings imply that the ionizing budget in the EoR was
likely dominated by UV-faint, low-mass and dustless galaxies.
