How to understand linkrel = "alternate" media = "handheld" href = "target "?

How do I understand linkrelalternatemediahandheldhreftarget? Poor language skills, how to understand link rel = "alternate" media = "handheld" href = "target"

This is the HEADER part embedded in a common webpage page. tell the search engine that the mobile phone version of the page is located in the href = "target" path?

If http://www.domain.com/article/123456.php is present on the home page
Relative phone version page is http://m.domain.com/article/123456.php

How to write href = "target" here? (It seems that target refers to the relative path. this second-level domain name ...)
In addition, how do I set the url rewrite. htacess file? Are the two article directories consistent? Or set separately? If they are consistent, then 123456. php is the same file. does php load different JS and CSS la s based on $ _ SERVER ['http _ USER_AGENT '] to distinguish between a common webpage and a mobile webpage?

Thank you.

Reply to discussion (solution)

Rel = "alternate"
Alternative version of the alternate document (such as printing pages, translations, or images ).

Media = "handheld"
Handheld device (small screen, limited bandwidth ).

Href = "target"
Open the linked document in the target framework

Still do not understand.
Rel = "alternate" media = "handheld" href = "target" must be added? Does it tell the search engine that the mobile phone version of this page is located at href = "target "?
For more information, see the document. the href = "target" is a relative path, not in the http: // format. how can I specify the m.domain.com second-level domain name?

Still do not understand.
Rel = "alternate" media = "handheld" href = "target" must be added? Does it tell the search engine that the mobile phone version of this page is located at href = "target "?
For more information, see the document. the href = "target" is a relative path, not in the http: // format. how can I specify the m.domain.com second-level domain name?
1) You do not need to add.
2) the designation of a second-level domain name is irrelevant to the domain name. it is only related to the root directory of your space.