Ah, OK - so you're referring to the column width for the attribute list. By default these lists are set with a specific column width (222 pixels in this case), if the windowlist control (https://www.fantasygrounds.com/refdoc/windowlist.xcp) is resized so that it's width allows for another column to be added, it will add another column with the same fixed width:
https://dl.dropboxusercontent.com/u/39085830/Screenshots/Fantasy%20Grounds/CoreRPG%20charsheet%20wide%201.jpg
If you want to dynamically change the width of the columns then you'll need to decide on a fixed number of columns - let's go with 2 in this case. Then, code needs to be written that detects when the window gets resized and changes the width of the columns using the setColumnWidth method based off the new width of the windowlist control: https://www.fantasygrounds.com/refdoc/windowlist.xcp#setColumnWidth
https://dl.dropboxusercontent.com/u/39085830/Screenshots/Fantasy%20Grounds/CoreRPG%20charsheet%20wide%202.jpg
The disadvantage if this is that if you have a lot of entries then resizing the width doesn't give you more columns, just two wider columns, and you'll have to resize the length (height) of the window or use the scrollbar. So, it's basically a design decision: dynamic width with a fixed number of columns, or dynamic number of columns with a fixed width.
To do the dynamic 2 column width resizing shown in the second screenshot above you'll need to modify the <template name="list_charmaincategory"> in campaign\template_char.xml as follows (code in red):
<template name="list_charmaincategory">
<windowlist>
<class>char_main_category</class>
<datasource>.maincategorylist</datasource>
<columns width="222" filldown="true" />
<allowcreate />
<allowdelete />
<sortby><field>label</field></sortby>
<script>
function onInit()
window.onSizeChanged = resizeColumns;
end
function resizeColumns()
local w, h = window.getSize();
setColumnWidth(math.floor(w/2)-40);
end
function onListChanged()
update();
end
function update()
local sEdit = getName() .. "_iedit";
if window[sEdit] then
local bEdit = (window[sEdit].getValue() == 1);
for _,wCategory in ipairs(getWindows()) do
wCategory.idelete.setVisibility(bEdit);
wCategory.attributes_iadd.setVisible(bEdit);
wCategory.attributes.update(bEdit);
end
end
end
function addEntry(bFocus)
local w = createWindow();
if bFocus then
w.header.subwindow.label.setFocus();
end
return w;
end
</script>
</windowlist>
</template>