consistent PHP function names?

One thing that's always bothered me about PHP is that the function names are not terribly consistent. For example, when are underscores okay? strip_tags() has an underscore but stripslashes() does not. Also, should inverse functions be named appropriately? htmlentities() and html_entity_decode() are inverse functions. But seems to make more sense to rename htmlentities() to html_entity_encode(). Something like a class[_subclass1[_subclass2[...]]]_method nomenclature makes sense. Then you have really weird stuff. For example, md5() is listed as a "string function" since it takes a string, calculates the MD5 hash, and returns said hash. Makes sense. Then you have md5_file(), which takes a filename, calculates the MD5 hash of the file's contents, and returns said hash. But md5_file() is listed as a "string function". To me, it makes more sense to be classified as a "filesystem function", and maybe even rename the function to file_md5(). Thoughts?