Using popular choices: Meta tags and web search
If you can write well and maintain accurate meta tags (e.g., descriptive titles and information for search bots), Google can more accurately crawl, index, and display your website in search results. Meta tags provide information to a variety of clients (e.g., browsers and search engines). Remember that each client may only parse the meta tags useful to that specific client while ignoring others (even though they might have other purposes).
Below is how Google parses the meta tags from the following HTML page:
```html
Traditional Swiss Cheese Fondue Recipe
Google uses this tag; site administrators should pay close attention to its accuracy.
Google uses this tag; our search results will display it.
Google does not use this tag, nor do other major search engines.
Optional; used by Google Webmaster Tools.
Optional.
```
```html
This tag provides a short description of the current page. In many cases, this description will be displayed as a page summary (snippet) in Google's search results. For more details, please refer to our blog post "Use better meta descriptions to improve page summaries" and the help center article "How to change the title and description of your site." Although the description meta tag is optional and does not affect your ranking, a good description can produce a better page summary, which in turn can help improve the quality of our search results and the number of visitors to your webpage.
Page Title
Technically, the title tag is not a meta tag, but it is often used alongside the "description" tag. The content of this tag (i.e., the title) is generally displayed in search results (and also visible when users browse webpages or check bookmarks using their browser). For more information about the title tag, see our blog post "For visitors or for search engines?" especially "Make the most of your webpage titles."
```html
These meta tags control how search engines crawl and index pages. The "robots" meta tag specifies rules applicable to all search engines, while the "googlebot" meta tag specifies rules only for Google. Google understands the following values (when specifying multiple values, separate them with commas):
- noindex: Prevents the webpage from being indexed (see "Use meta tags to block or delete webpages")
- nofollow: Do not find and crawl new webpages via links on the current page (also see "Use meta tags to block or delete webpages")
- nosnippet: Do not display a page summary in search results (see "Prevent displaying or deleting page summaries")
- noodp: Do not use text from the Open Directory Project (also known as dmoz.org) to generate titles or page summaries for this page (see "How to change the title and description of your site?")
- noarchive: Do not display a "Cached" link when showing this webpage in search results (see "Prevent displaying or deleting cached webpages")
- unavailable_after:[date]: Remove this webpage from search results after the specified date and time (see "Robots Exclusion Protocol: Now more flexible")
When this tag is completely omitted or when content="all" is specified, the default rule is "index, follow." For more information about the "robots" meta tag, see "Use robots meta tags." As an example, you can now specify this information in the header of your page through the "X-Robots-Tag" HTTP header instruction. This is particularly useful if you want to fine-tune crawling and indexing for non-HTML files such as PDFs, images, or other types.
```html
When we recognize that the content of a page is not written in a language that the user might want to read, we often provide a link in the search results to automatically translate your webpage. Generally, this gives you the opportunity to offer unique and impressive content to a wider audience. However, in certain situations, you may not want your webpage translated. With this meta tag, you can indicate that you do not want Google to provide a "Translate this page" link. This meta tag typically does not affect the page's ranking for any specific language. For more information, see the "Google Translate FAQ."
```html
This is a specific meta tag for Google Webmaster Tools used on high-level pages of your site to verify the ownership of a site within Webmaster Tools (another verification method involves uploading an HTML file). The value you set for "content=" is provided by your Webmaster Tools account. Note that the content value of this meta tag (including case sensitivity) must exactly match the value provided by your account, regardless of whether you change the tag from XHTML to HTML or whether the format of your tag matches your webpage. For more details, see "How to verify your site by adding a meta tag to your homepage?"
```html
This meta tag defines the content type and character set of the page. When using this meta tag, the value of the content attribute must be enclosed in quotes; otherwise, the character attribute may be misinterpreted. If you decide to use this meta tag, ensure that your content actually uses the specified character set. Some interesting data about the use of this meta tag can be found in "Google's Web Author Statistics."
```html
This meta tag redirects users to a new URL after a certain period of time and is sometimes used as a simple redirection method. Not all browsers support this kind of redirection, and it may confuse users. If you need to change the URL of a page displayed in search engine results, we recommend using a server-side 301 redirect. Additionally, the W3C's "Web Content Accessibility Guidelines and Techniques 2.0" lists this tag as one that should be deprecated.
(X)HTML and Case Sensitivity
Google can read both HTML-style and XHTML-style meta tags (regardless of the encoding used on the webpage). Furthermore, the case of meta tags generally does not matter—we treat and as the same. However, the "verify-v1" meta tag is an exception as it is case-sensitive.
"Revisit-after" vs. Sitemap's "lastmod" and "changefreq" Tags
Occasionally, webmasters unnecessarily include the "revisit-after" tag to speed up a search engine's crawling, but unfortunately, this meta tag is mostly ignored. If you want to inform search engines about changes to your pages, you can submit an XML sitemap. In this file, you can specify the last modification date ("lastmod") and the change frequency ("changefreq") of your site's URLs.
Article Source: http://www.01cm.com.cn/google-optimize/144/
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