HTML: types of attribute values
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Many HTML
attributes accept specific types of input, including the following:
Value
|
Description
|
#mapname
|
Name of client-side
image-map, i.e. a hash character (#) plus the name of a <map> element
|
character
|
A single keyboard
character (e.g. as per the accesskey
attribute)
|
character_set
|
A character encoding
(i.e. way of representing characters that will be recognised by a receiving
computer), such as:
-
UTF-8: Unicode
-
ISO-8859-1: character
encoding for Latin alphabet
|
CSSclass
|
Name of a CSS class.
These must begin with a letter A-Z or a-z, which can be followed by letters
(A-Z or a-z), digits (0-9), hypens (“-”) and underscores (“_”). In HTML all
such values are case-insensitive, i.e. class names of “abc” and “ABC” are
treated as synonymous.
|
CSSstyle
|
A CSS style
definition
|
datalist_id
|
Id (identifier) of
relevant <datalist>
element
|
date
|
A date
|
elementID
|
The id (identifier)
defining the associated element
|
file_extension
|
A file extension
starting with a full stop, e.g. .png,
.jpg, .pdf, .doc
(e.g. used for the accept
attribute)
|
filename
|
File name of a resource
|
formID
|
The id defining the
associated form
|
framename
|
A named frame (i.e. <iframe>
element)
|
groupname
|
Name of group of
commands
|
header_id
|
Id of a header cell
|
heightxwidth
|
One or more sizes (in
pixels), in the form e.g. sizes="16x16"
or sizes="16x16 32x32".
|
HTML_content
|
HTML content
|
HTTPmethod
|
Either get or post.
These have the following characteristics:
-
get. Use the HTTP ‘get’
method. This includes the form-data in the URL in name/value pairs. The
length of the URL is limited and hence the values transmitted will be public
(even if the website is accessed using an https call), but users can bookmark
the resulting call
-
post. Use the HTTP
‘post’ method. This includes the form-data in the HTTP request, i.e. not in
the URL, and is not subject to the same size limitations as the ‘get’ method,
but cannot then be bookmarked by users
|
inputfieldname
|
Name of an input field
|
integer
|
An integer
|
language-code
|
Language of text in
linked document. The language code is either an ISO 639-1 two letter language
code (e.g. “en”) or such a code followed by a dash and then a two letter ISO
country code (the latter can be used if different countries recognise
different versions of the same language, e.g. “en-gb” versus “en-us”)
|
machine-readable
format
|
Machine-readable
content
|
media-query
|
Media or device type
|
media_type
|
A valid media type, see
e.g. http://www.iana.org/assignments/media-types/media-types.xhtml
(e.g. as per accept
attribute)
|
MIME-type
|
MIME type of resource
|
name
|
Name of element,
attribute or (for <meta>
elements) metadata item
|
no value
|
I.e. element should be
left black, however see below regarding attribute minimisation and XHTML.
|
number
|
A number (sometimes
only an integer is acceptable, e.g. for the cols attribute,
sometimes a floating-point value is also acceptable), usually in the form of
a string (enclosed in quotes) representing the number
|
percentage
|
A percentage, e.g. 30%
|
regular-expression
|
Regular expression
(against which e.g. an input is compared)
|
text
|
Text
|
URI
|
Uniform Resource
Identifier, see below.
|
URL
|
i.e. Uniform Resource
Locator. These can be:
-
Absolute, pointing to a specific webpage, e.g. http://www.nematrian.com/Introduction.aspx,
or
-
Relative, pointing to a file relative to some base, usually the
directory or website within which the page accessing the URL is position,
e.g. example.htm
|
x1, y1, x2,
y2
|
Typically involve
coordinates as per the coords attribute
|
YYYY-MM-DDThh:mm:ssTZD
|
A date (in a specific
machine and location independent format)
|
When a value the attribute can take is shown as the same as
its own name then this is a Boolean-style attribute, meaning that in HTML the
attribute should either be mentioned (but assigned no value), in which case the
attribute applies, or be absent, in which case the attribute does not apply. In
XHTML, such attribute minimisation is not allowed, and the attribute
needs to be defined explicitly, taking as its value its own name, e.g. <video …
autoplay="autoplay">…</video>.
Event attributes (which usually have the form on…) take values which are JavaScript
functions.
Uniform Resource Identifiers (URIs):
‘URI’ stands for ‘Uniform
Resource Identifier’. The possible set of parts a URI can contain are
illustrated by the following:
http://username:pword@www.example.org:80/path/file.aspx?a=23&b=has+spaces#anchor
A URI encoded string has
each instance of certain characters replaced by one, two, three or (rarely)
four escape sequences representing the UTF-8 encoding of the character. encodeURI escapes all characters
except for the following (so it does not encode characters needed to formulate
a complete URI as above, or a few additional ‘unreserved marks’ which do not
have a reserved purpose as such and are allowed in a URI ‘as is’):
A-Z a-z 0-9 ; , / ? : @ & = + $ - _ . ! ~ * ' ( ) #
There are four global
JavaScript
methods that convert strings into URIs and vice versa (six if depreciated
methods are included).
encodeURI() escapes all characters except for the
following (so it does not encode characters needed to formulate a complete URI
as above, or a few additional ‘unreserved marks’ which do not have a reserved
purpose as such and are allows in a URI ‘as is’:
A-Z a-z 0-9 ; , / ? : @ & = + $ - _ . ! ~ * ' ( ) #
encodeURIComponent() also escapes reserved characters, so
escapes all characters except:
A-Z a-z 0-9 - _ . ! ~ * ' ( ) #
escape() (now depreciated, use encodeURI or encodeURIComponent
instead) encodes all characters with the exception of * @ - _ + . /
decodeURI(), decodeURIComponent()
and unescape() are the inverses
of encodeURI(), encodeURIComponent() and escape() respectively.
If you want to encode a string but avoid encoding square
brackets (these are becoming reserved characters for IPv6) then it is
recommended that you use a JavaScript
statement like:
encode(str).replace(/%5B/g,'[').replace(%5D/g,']')
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