REBOL 3 Docs | Guide | Concepts | Functions | Datatypes | Errors |
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Tags are used in HTML and other markup languages to indicate how text fields are to be treated. For example, the tag <HTML> at the beginning of a file indicates that it should be parsed by the rules of the Hypertext Markup Language. A tag with a forward slash (/), such as </HTML>, indicates the closing of the tag.
Tags are a subset of series, and thus can be manipulated as such:
a-tag: <img src="mypic.jpg">
probe a-tag
<img src="mypic.jpg">
append a-tag { alt="My Picture!"}
probe a-tag
<img src="mypic.jpg" alt="My Picture!">
Valid tags begin with an open angle bracket (<) and end with a closing bracket (>). For example:
<a href="index.html"> <img src="mypic.jpg" width="150" height="200">
The to-tag function converts data to the tag! datatype:
probe to-tag "title"
<title>
Use [bad-link:functions/build-tag.txt] to construct tags, including their attributes. The [bad-link:functions/build-tag.txt] function takes one argument, a block. In this block, the first word is used as the tag name and the remaining words are processed as attribute value pairs:
probe build-tag [a href http://www.rebol.com/]
<a href="http://www.rebol.com/">
probe build-tag [
img src %mypic.jpg width 150 alt "My Picture!"
]
<img src="mypic.jpg" width="150" alt="My Picture!">
Use tag? to determine whether a value is an tag! datatype.
probe tag? <a href="http://www.rebol.com/">
true
As tags are a subset of the series pseudotype, use series? to check this:
probe series? <a href="http://www.rebol.com/">
true
The form function returns a tag as a string:
probe form <a href="http://www.rebol.com/">
{<a href="http://www.rebol.com/">}
The mold function returns a tag as a string:
probe mold <a href="http://www.rebol.com/">
{<a href="http://www.rebol.com/">}
The print function prints a tag to standard output after doing a reform on it:
print <a href="http://www.rebol.com/">
<a href="http://www.rebol.com/">
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