A stringlist is a list that can contain a number of elements, all have to be of type string. see Using Lists for more information.
For Quest 5.3 and earlier, the format in an ASLX file is this:
<mylist type="list">one; two; three</mylist>
As of Quest 5.4, the same list is expressed like this:
<mylist type="list">
<value>one</value>
<value>two</value>
<value>three</value>
</mylist>
In Quest 5.4, you can still use the older semi-colon separate format with “simplestringlist”:
<mylist type="simplestringlist">one; two; three</mylist>
There is more on lists here.