The alignment definitions can be looked up in the file Data\Editor\Templates\Alignments\Alignment.lsx
Although I do not fully understand everything in there, my assumption is that in an entry like
<node id="Relation">
<attribute id="Source" value="Hero" type="22" />
<attribute id="Target" value="Evil" type="22" />
<attribute id="Value" value="0" type="4" />
</node>
the value="0" means that a meeting of characters in these two categories results in an immediate combat start as soon as one sees the other.
The 'Evil NPC' Sniper mentioned can be found in the file too
<node id="Entity">
<attribute id="Alignment" value="Evil" type="22" />
<attribute id="Name" value="Evil NPC" type="22" />
</node>
And for example
<node id="Relation">
<attribute id="Source" value="Hero" type="22" />
<attribute id="Target" value="Neutral" type="22" />
<attribute id="Value" value="50" type="4" />
</node>
makes sure that the Orcs in Hunter's edge, who are mostly in the category
<node id="Entity">
<attribute id="Alignment" value="Neutral" type="22" />
<attribute id="Name" value="DAF_VillageBO_Orc" type="22" />
</node>
do not attack you immediately, and
<node id="Relation">
<attribute id="Source" value="DAF_VillageBO_Torturers" type="22" />
<attribute id="Target" value="DAF_VillageBO_Prisoners" type="22" />
<attribute id="Value" value="50" type="4" />
</node>
makes sure, the torturer's in the Hunter's Edge prison do not slaughter the prisoners, so that there is still some story to tell.
This alignment can be changed by script, because at some point, there is a time for fighting in Hunter's edge ;-)