User:Andy Dingley/sandbox

WP:MATH

$$ w v^2 = k d^3 \left( \frac {t}{d} \right) ^ n $$

$$ \omega_A = \frac {50 \ ms^-1 }{ 50 \ m } = 1 s^-1$$

$$ \omega_B = \frac {50 \ ms^-1 \times cos(\theta) }{ 50 \ m \ / \ cos(\theta) } = \frac {50 \ ms^-1 \times 0.5 }{ 50 \ m \ / \ 0.5 }  = \frac {25 \ ms^-1}{100 \ m} = 0.25 s^-1$$

LED
WP:MATH

$$R = \frac {V_{battery} - V_{forward}} {I_{LED}}$$

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semweb
Semantic HTML is a contemporary best-practice coding style for HTML.

The core of Semantic HTML is the separation of content and presentation, by expressing the content in HTML and the presentation by CSS. The content's representation in HTML should follow the semantics of the underlying document.

Principles of Semantic HTML

 * Content semantics are expressed through HTML markup
 * Presentation is expressed by attaching CSS to the HTML.
 * HTML elements are used appropriately for their existing semantics, not mis-used because of any coincidental presentation effects they might have.
 * Semantic HTML should be well-formed and valid, as this allows the HTML's semantics to be read unambiguously and correctly.

Practicalities of Semantic HTML
The principles are two-fold, separating content and presentation and then enhancing the appropriate parts of each by placing as much as possible of the semantics into the "content" part (HTML) and as much as possible of the "presentation" into the CSS. Both of these are very much a grey area though: a total separation is impractical.

Most of the practical benefits of Semantic HTML arise from what's removed, not what's added. Removing the presentation from the HTML makes for a far simpler authoring task. This is often sufficient to make hand-coding with a text editor practical, rather than requiring a WYSIWYG tool simply to manage the multiplicity of  cells.

Advantages of Semantic HTML
The main advantage of Semantic HTML is for authoring, and human authoring with a text editor in particular (rather than WYSIWYG).

It's also typical for many sites that there is an underlying structure reflected in most pages that chanegs little between them. This controls the presentation more than the variations of each page (and so the presentation is consistent across all the pages in the site).

Requirements for Semantic HTML
Semantic HTML became a real possibility in 1997, with the HTML 4.0 and CSS standards. These permit the separation of content and presentation.

Before this time, HTML 3.2 merged the content and presentation of web documents into a single HTML format. It was impossible to separate them.

Even now, 10 years later, HTML 4.0 is still poorly adopted by "typical" web sites.

Semantic HTML and the Semantic Web
Semantic HTML has surprisingly little to do with the Semantic Web. Neither is a requirement for the other, nor does either even benefit much from the other.

Semantic HTML is restricted by the minimal semantics possible within HTML. These are not generally sufficient to communicate semantics in a useful manner.

The Semantic Web (in its current state of development) is also about the web of pages, more than the individual page. Identity and characterisation of a page is more important than the internal structure of the page. If this cataloguing metadata can be extracted by other means (such as RDFa) this is sufficient to build the Semantic Web, without needing to analyse the page content itself.

Semantic HTML is an underlying foundation for making pages that are comprehensible automatically, in that they avoid the presentational HTML that would otherwise make this impractical. Achieving real automatic comprehension though will require additional annotation before it becomes really effective.

Implementation of Semantic HTML
Semantic HTML is basically simple. Most of its practice is about avoiding the bad, rather than extra effort to achieve the good.

Avoidance of presentational HTML Elements
A Strict HTML DTD should be used, rather than Transitional. This itself excludes many of the purely presentational elements (font, basefont, u, s, strike). should obviously be avoided entirely.

tags
The status of these elements (which are still in the HTML 4.01 Strict DTD) is often debated: Should they be categorised with  as having a semantic meaning in addition to their obvious presentational implication?

Abuse of HTML Elements
The greatest problem to avoid is the abuse of HTML elements.

Incidental presentational effects
Non-semantic HTML

Semantic HTML

Even this is debatable over the level of its "semanticness".

Annotation of anonymous elements
is also better than or (in most situations).