Therefore, another term, namespace-well-formed , is defined in the Namespaces in XML 1. Colloquially, the term well-formed is often used where namespace-well-formed would be more precise. However, this is a minor technical manner of less practical consequence than the distinction between well-formed vs valid XML described in this answer.
Well formed XML is XML that has all tags closed in the proper order and, if it has a declaration, it has it first thing in the file with the proper attributes. Python Javascript Linux Cheat sheet Contact. Is there any difference between 'valid xml' and 'well formed xml'? One may also ask, what is a valid XML file? These rules are: A well-formed XML document must have a corresponding end tag for all of its start tags.
Nesting of elements within each other in an XML document must be proper. Any elements defined in a DTD can be used in these documents, along with the predefined tags and attributes that are part of each markup language. XML tags are case-sensitive. All XML elements must be properly nested. All XML documents must have a root element. Attribute values must always be quoted. With XML, whitespace is preserved. We developers can used the XML data files to generate the dynamic content by applying different Style sheets.
XML is also used to develop the content management systems. Many companies are using XML files to write the documents. XML is used to transport and the data on internet and between different programs. It defines the document structure with a list of legal elements. There are a number of schema languages, many of which are themselves XML-based. So if you use an attribute improperly, you violate the DTD and aren't valid. XML is well-formed if meets the requirements for all XML documents set out by the standards - so things like having a single root node, having nodes correctly nested, all nodes having a closing tag or using the empty node shorthand of a slash before the closing angle bracket , attributes being quoted etc.
Being well-formed just means it adheres to the rules of XML and can therefore be parsed properly. This obviously differs from case to case - XML that is valid against one schema won't be valid against another schema, even though it is still well-formed.
If XML isn't well-formed it can't be properly parsed - parsers will simply throw an exception or report an error. This is generic and it doesn't matter what your XML contains.
Only once it is parsed can it be checked for validity. This domain or context dependent and requires a DTD or schema to validate against. For simple XML documents, you may not have a DTD or schema, in which case you can't know if the XML is valid - the concept or validity simply doesn't apply in this case.
Of course, this doesn't mean you can't use it, it just means you can't tell whether or not it's valid. If an XML document follows all these rules, it is said to be well-formed document and XML parsers can be used to parse and process such documents. This includes the parent-child relationship details, attribute lists, data type information, value restrictions, etc.
All valid XML documents are well-formed, but the reverse is not always true. Well-formed XML documents do not necessarily have to be valid.
Based on the theory: "Well Formed" vs. This is a description of the content for a family of XML files. This is part of the XML 1.
Validation is the process of checking a document against a DTD more generally against a set of construction rules. Briefly a DTD defines all the possible elements to be found within your document, what is the formal shape of your document tree by defining the allowed content of an element; either text, a regular expression for the allowed list of children, or mixed content i.
The DTD also defines the valid attributes for all elements and the types of those attributes. Stack Overflow for Teams — Collaborate and share knowledge with a private group. Create a free Team What is Teams? Collectives on Stack Overflow. Learn more. See the next section for more detail.
The encoding used in the above example, UTF-8, is a Unicode-based encoding scheme. Unicode at first supported bit characters, as opposed to ASCII's 8-bits — this bit format could encode different characters, taken from most of the known languages. This has since been expanded to 32 bits. The simplest encoding mapping this to 4 fixed bytes is called UCS To represent these characters more efficiently, variable length encodings are typically used instead: UTF-8 and UTF The Basic Multilingual Plane characters in the range can be encoded using bit words.
For more than 16 bits, characters can be encoded using pairs of words and the reserved DDFFF range. Subsequent characters can be encoded using variable encoding. Here are some examples:.
Note that the first bits until the first 0 are used to indicate how many bytes set of 8 bit are used to encode the character. Subsequent bytes for the same character encoding begin with The data bits follow each of these header bits represent by v's in the above examples in each byte.
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