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Also known as: Ymodem Y-Modem is an error-correction protocol used in the transfer of serial data files between modems. Y-Modem is based on the earlier X-Modem protocol, but has the additional feature of being able to cope with a batch transmission mode, in which a number of files can be sent with one command. For greater efficiency Y-Modem can also handle data with a variable block size of up to a maximum 1024 bytes (1 kB). During transmission, the size of text and binary files is included in the Y-Modem header, so that the exact file length will be retained after transfer. The error detection method in Y-Modem is cyclic redundancy check (CRC). A later version of Y-Modem, Y-Modem-G, transmits data in a continuous stream and does not acknowledge the blocks successfully received; it is only the blocks with detected errors that cause a negative acknowledgement (NAK), thus prompting the resending of data
XHTML (a merger of XML and HTML) is an updated HTML standard introduced to help tidy up all the developments and additions to original HTML. Over the years, different browsers added features and offered increased functionality, which all had their own proprietary manifestation in HTML. This led to a mish mash of tags and markup that often led to web authors putting in duplicate attributes and code in order to make sure that a page looked the same in different browsers browsers. XHTML is a unifying standard from the W3C that brings the XML benefits of easy validation and troubleshooting to HTML, which not only helps developers but also makes the pages easier to read for programs such as mobile browsers. There are three variations of XHTML, the most common of which is Transitional. XHTML Transitional is a stepping stone from the deprecated HTML standardsL, and as such is fairly permissive, allowing many old and proprietary attributes, although Transitional stipulates that all tags must have both opening and a closing markup and be correctly nested. XHTML Strict is a more rigourous standard that removes all the ’chaff’ gathered by HTML not ruled out in Transitional, and is what web authors should strive toward. Finally, XHTML Frameset is similar to XHTML Transitional, but allows for the use of frames.
extensible markup language