Why shouldn't I use underscore within folder names?

Using underscores within folder names can sometimes cause ambiguity and lead to broken URLs on your website. The reason is that, for example, a folder named u_2 (after the band, of course) can also be parsed as an attempt to "underlay" a resource named "2" over the base image.

To be on the safe side, you should make sure you stick to at least one of the following principles: 

• Avoid using underscores "_" within names you give to your folders. You can use dash "-" as a delimiter instead.
• Use at least 4 characters prior to the first underscore occurrence, e.g. abcd_1234.
• Use versions to isolate the public ID from the transformation section.