  An extremely careful analysis of the forest of weak metal-line systems at z ~
2 has allowed the separation into individual `single-phase ionization'
components with accurate parameters. The systems typically span several hundred
km/s and within each the components show a strong coherence in their ionization
properties. A general feature of the observed systems is the presence of high
ionization broad components which co-exist in velocity space with more
numerous, narrow, lower ionization components. From a sample of components
extending to z ~ 3.5, taken either individually or as system totals, no rapid
evolution is found in the column density ratio N(Si IV)/N(C IV), contrary to
previous indication of a large change near z = 3.1. Comparisons of component
ion ratios including Si IV, C IV, C II and Si II from the sample at z ~ 2 with
CLOUDY derived values using several model ionizing spectra show the general
dominance of the metagalactic ionizing background over local stellar radiation
and give Si/C distributed 1-3 times the solar value. Indications of the
evolution of structure are highlighted.
