Files are included based on the file path given or, if none is given, the include_path specified. If the file isn't found in the include_path, include will finally check in the calling script's own directory and the current working directory before failing. The include construct will emit a warning if it cannot find a file; this is different behavior from require, which will emit a fatal error.
#if PHP_WIN32 /* This should count as an absolute local path as well, however IS_ABSOLUTE_PATH doesn't care about this path form till now. It might be a big thing to extend, thus just a local handling for now. */ filename_length >=2 && IS_SLASH(filename[0]) && !IS_SLASH(filename[1]) || #endif