I’ve been curious about this for a while so I thought I would ask it here on stack. I was told to always lowercase my Sitecore placeholders by a consultant helping out on one of my projects.
I was new to Sitecore at the time, so I took it in stride and never really questioned it. However, as I’ve become more familiar with the system and how extensible and modular it can be, I really can’t imagine why this would be a requirement..?
There doesn’t appear to be any documentation on the subject, however, Sitecore themselves seem lowercase their placeholders in every example site I’ve ever seen.
The topic is metioned a few times on the web including right here on stack, however, the question remains: WHY?
You may be referring to a specific version of Sitecore that had a bug in it. There is currently no requirement for using only lowercase. I suspect when Sitecore’s dependency injection / layout engine runs, is compares the placeholder keys on the layout to the controls bound and ignores the cases when matching up placeholder keys.