I'll explain it from the top down and then tell you how to construct the fields and thumbnail text.
The whole idea of this is to build new fields for each line we want to display. For example, for the lines to represent the Album, I built 3 new fields, asl1, asl2, and asl3. Each are calculated fields that break up the [Album] field into pieces. Up to 3 pieces, one per field.
Then we'll build a thumbnail expression which contains asl1, asl2, asl3 and our album artist fields also.
Here are the various fields I have constructed. They are all string type fields with calculated data:
asreg: This controls the number of characters used to split the fields into multiple lines. Because of the regex, it splits on word boundaries at, or under the number specified. Change the two "28" below to whatever number of characters you want to split your lines at.
/#^(.{1,28})(\s(.{1,28}))?(\s(.+))?$#/
asl1: This and the next two are the 3 lines that [Album] are broken into.
Regex([Album],[asreg],-1,0)[R1]
asl2:
Regex([Album],[asreg],-1,0)[R2]
asl3:
Regex([Album],[asreg],-1,0)[R4]
aaal1: This and the next one are the two lines that [Album Artist (auto)] are broken into.
Regex([Album Artist (auto)],[asreg],-1,0)[R1]
aaal2:
Regex([Album Artist (auto)],[asreg],-1,0)[R2]
Now that we have all of our custom fields defined, we need to customize the thumbnail text using these lines. Here's a simple one that I'm using in the screen shot:
listbuild(1,/#
#/,[aaal1],[aaal2])
listbuild(1,/#
#/,[asl1],[asl2],[asl3])
That expression has two embedded newlines in it. So you probably want to copy and paste it directly. The newlines make the expression display each field on a different line.
That should be all you need to get started. This technique can be extended to other large fields if you like.
Brian.