How has the previous user created this format in Illustrator?

[Emma303408072y74]

Hi there!

I need to create a long form infogaphic for an EDM and I've inherited the file from last year's designer.

I've worked in Illustrator for a few years now but its the first time I've come across this formatting. 

Could somoene please tell me what it's called and how I can recreate it? 

[Bobby Henderson · Accepted solution]

Those blocks are image slice boundaries made with the Slice tool.