Some resource locations are case sensitive (e.g. a typical UNIX file system), whereas others are not (e.g. a typical Windows file system).
Incorrectly specifying the case sensitivity of a resource location can lead to confusing or hard to predict behaviour, including the miss-alignment of topics for comparison, not being able to locate specified resources, unexpected deletion of files, and exceptional termination of the comparison. Having said this, if the case of the URI's, as specified by their hrefs within a DITA document, is consistent with that of the underpinning resource location, then none of these issues should occur.
We assume that URI's of two distinct resources do not differ only in their case, and that the case of the 'href' references within a document are consistent with that of the underpinning resource location; i.e. the 'href' references are specified using precisely the same case as that of the resource location that they are referencing.