Unicode Explained

tags <p> and </p>. UTR #20 recommends that an occurrence of LS or PS in marked-

up text be treated as whitespace—i.e., as equivalent to a space.

According to UTR #20, the Bidi embedding controls U+202A..U+202E (see Chapter

5) are “strongly discouraged” in the HTML 4 specification, which however actually

just warns about possible conflicts between those controls and equivalent markup. It

recommends that preferably one or the other should be used exclusively, and adds:

The markup method offers a better guarantee of document structural integrity and alle-

viates some problems when editing bidirectional HTML text with a simple text editor,

but some software may be more apt at using the UNICODE characters. If both methods

are used, great care should be exercised to insure proper nesting of markup and direc-

tional embedding or override, otherwise, rendering results are undefined.

UTR #20 suggests that markup be used instead of the controls on the following

grounds:

The embedding controls introduce a state into the plain text, which must be maintained

when editing or displaying the text. Processes that are modifying the text without being

aware of this state may inadvertently affect the rendering of large portions of the text, for

example by removing a PDF [= Pop Directional Formatting].

Although this recommendation is usually adequate, there are situations where markup

cannot be used ...