Nautical Chart Convention (or Standard ?) from S-57 Data

[twal]

Hi,

I am trying using MapServer Welcome to MapServer — MapServer 5.6.3 documentation to render S-57 data.
(MapServer is a web map server which can serve maps from a web server to various client applications. An integration of OpenStreetMap is also possible.)

Is there any good document for nautical chart standard or convention of color, symbol, label? how openCPN render S-57? all hard-coded?

For example, I use openCPN to show only DEPARE(A depth area is a water area whose depth is within a defined range of values.) layer from a S-57 map.

A DEPARE area has two attributes: DRVAL1 and DRVAL2 representing The min. and max. value of a depth range.

One of areas from my S-57 has a depth range from 10 (DRVAL1) to 20 (DRVAL2) meters. However openCPN will show a label "14" on it. It seems not just an average value.

how about the standard from IMO or IHO?