In FileMaker Pro 16, it appears that the GetLayoutObjectAttribute function will return rewritten equivalent of data as html, regardless of content. An example would be, with a web viewer object named "web", and a function call of GetLayoutObjectAttribute ( "web" ; "content" ):
The actual data:
<input type="text" name="myName" value="123" />
What the function returns:
<input type="text" name="myName" value="123">
Note that not only did additional html tags get inserted, but also some elements get rewritten, as is the case with the closing slash in the "input" type. It can throw off pattern matching in solutions that worked in previous versions.