[joropito]

This is my first tutorial.

After interpreting trigger.cpp (from HLDS), I decided to make this tutorial.

EngFunc_EntitiesInPVS (maybe the same for EngFunc_FindClientInPVS)
It returns an entity in PVS (potential visible set) of a player.
It never returns worldspawn.

In that entity returned, you have a set of chained entities using pev_chain.

Example

public whatisonPVS(id)
{
    static next, chain;
    static class[32];

    next = engfunc(EngFunc_EntitiesInPVS, id);
    while(next)
    {
        pev(next, pev_classname, class, charsmax(class));
        chain = pev(next, pev_chain);

        server_print("Found entity in player (%i) PVS: ent(%i) class(%s)", id, next, class);
        if(!chain)
            break;
        next = chain;
    }
}

So this function iterates over and over every entity until pev_chain is NULL.