Power Query Splitter syntax

Hi,
bit of theory can someone explain the parts of the

Splitter.SplitTextByCharacterTransition

I get how it works when used like this;

  Table.SplitColumn( Source, "Text", Splitter.SplitTextByCharacterTransition(  { "a".."z"}, {"0".."9"} ) )

so when it goes from lower case letter to number ( ok txt number), but if I use the interface;

 Table.SplitColumn(Source, "Text", Splitter.SplitTextByCharacterTransition((c) => not List.Contains({"0".."9"}, c), {"0".."9"}), {"Text.1", "Text.2"})

so does (c)=> represent each value of the source? which produces a list of true / false ? if anyone can explain or knows of a post / blog / information on how this breaks down I would be interested . Thanks.

Richard