HTML 5th Edition

by Elizabeth Castro

Elements are block or inline; block elements are displayed on new lines, while inline elements are not. This is the difference between div and span.
If you save your document in UTF-8, and declare it as such when serving it, you don't have to use character references like &copy, with the exception of &amp for &.
XHTML requires the DOCTYPE and html, head, and body elements in a document, and that every attribute has a value (e.g. noshade="noshade").
If a browser finds a DOCTYPE, then it uses standards mode; otherwise, it uses quirks mode.
A stylesheet has multiple rules. Each rule is composed of a selector, and between the curly brackets, a collection of declarations separated by semicolons. Each declaration has a property name, followed by a colon, and one or more values.
CSS uses inheritance, specificity, and location to resolve rule conflicts:
Many CSS properties affect not only the elements defined by the selector but also their descendants; this is called inheritance.
If multiple rules apply to an element and conflict with each other, the more specific rules take precedence (e.g. a rule for an id overrides a class); this is called specificity.
If this cannot decide which rule to apply, the last rule takes precedence; this is called location.
When declaring the length of an element, em is usually equal to the element's font size.

Declare the page encoding in UTF-8 with <meta http-equiv="content-type" content="text/html; charset=utf-8" /> in the <head> element. Starting the document with <?xml version="1.0" encoding="UTF-8"?> will put IE6 into quirks mode.
The id attribute automatically turns the element into an anchor, to which you can directly link.
A span has no inherent formatting, while a div only has the line break as inherent formatting.
You can use the title attribute to add a tool tip to anything; to suppress IE from using alt as a tooltip for images, use an empty title, i.e. title="".

The tt element forces monospaced font; when displaying computer code, the code attribute is equivalent, but gives semantic meaning.
To strikethrough text, use the del element.
Use the abbr or acronym tag (if the abbreviation an be pronounced as a word) with the title attribute to explain their contents when hovering.

If a browser is asked to show a color outside its range, it can mix two colors (called ditherhing) or show the closest available one (called shifting).
The web-safe or browser-safe colors are the 216 colors that are not reserved by the browser and are supported by both Windows and Mac.
Each frame in GIF format is limited to 256 colors, although these colors can be selected from a much larger palete.
The PNG format is not limited to 256 colors, and like GIF is lossless and allows for transparency, but unlike GIF cannot have multiple frames.
The JPEG or JPG format, typically used for photos, uses lossy compression and so originals should be saved in a format like TIFF.

Add the width and height attributes to the img element so that the browser can display the text while the image loads.
Use the br element with the clear attribute so that the following elements will not display until the specified margin (left, right, or all) is clear.

Open a link in a new window by adding target="_blank" to the link element.
Links with the same value for target will all open in the same window.
Add the tabindex attribute between 0 and 32767 to links to define a custom tab order; links with the same index value are accessed in the order in which they appear.

A descendant selector of the form A B matches when an element B is an arbitrary descendant of some ancestor element A.
The universal selector is *, and A * B matches a B element that is a grandchild or later descendant of an A element.
The child selector of the form A > B matches when an element B is a child of an A element.
The adjacent sibling selector of the form A + B matches when an element B is an adjacent sibling of an A element.
The attribute selector A[foo] matches any A element with attribute foo set; A[foo~="bar"] restricts to only foo attributes containing bar, and A[foo="bar"] restricts to only foo attributes equal to bar.
Pseudo-classes select markup; the selector A:first-child chooses only the A elements that are the first child of some parent element.
When setting link properties, i.e. the a tag, define them in the order link, visited, focus, hover, active.
Pseudo-elements select content; the selector A:first-line or A:first-letter chooses the first line (which can change as the browser resizes) or first letter of any A element.

To change the marker, set the list-style-type property with values disc, circle, square, decimal, upper-alpha, lower-alpha, upper-roman, or lower-roman.
To use a custom image, set the list-style-image property with a value as the image URL; the image should be no larger than 15 x 15 pixels.
The dl element begins a definition list, suited for glossaries, where terms are in dt and definitions are in dd, alternating as necessary.
When styling nested lists, the selectors should reflect the types of nested lists, e.g. ol li and ol ol li.

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