4.4.1 Case Information

Each attribute definition includes information about case-sensitivity of its values. The case information is presented with the following keys:

• CS The value is case-sensitive (i.e., user agents interpret "a" and "A" differently).
• CI The value is case-insensitive (i.e., user agents interpret "a" and "A" as the same).
• CN The value is not subject to case changes, e.g., because it is a number or a character from the document character set.
• CA The element or attribute definition itself provides case information.
• CT Refer to the type definition for details about case-sensitivity.

If an attribute value is a list, the keys apply to each value in the list, unless otherwise indicated.

4.4.2 Basic Data Types

The document type definition specifies the syntax of SAPI element content and attribute values using SGML tokens (e.g., PCDATA, CDATA, NAME, ID, etc). See [ISO8879, ISO 8879:1986] for their full definitions. The following is a summary of key information:

CDATA is a sequence of characters from the document character set and may include character references (see also Character References). User agents should interpret attribute values as follows:

• Replace character references (see Character References) with characters;
• Ignore line feeds;
• Replace each carriage return or tab with a single space.

4.4.3 Text Strings

A number of attributes (%Text; in the DTD) take the text that is meant to be "human readable". Introductory information about attributes can be found in the tutorial discussion of attributes.

4.4.4 URIs

This specification uses the term URI as defined in [URI] (see [RFC1630]).

Note that URIs include URLs (as defined in [RFC1738] and [RFC1808]).

URIs are represented in the DTD by the parameter entity %URI;.

URIs in general are case-sensitive. There may be URIs, or parts of URIs, where case doesn't matter (e.g., machine names), but identifying these may not be easy. Users should always consider URIs case-sensitive (to be on the safe side).

4.4.5 Single Characters

Certain attributes call a single character from a set of document characters. These attributes take the %Character type in the DTD.

Single characters can be specified using character references (e.g. "&").

4.4.6 Character Data

Certain attributes call single document characters. These attributes take the %Text type in the DTD.

4.4.7 Dates and Times

[ISO8601] allows many options and variations in the representation of dates and times. The current specification uses one of the formats described in the [Datetime] profile for its definition of legal date/time strings ( %Datetime in the DTD).

The format is:  

YYYY-MM-DDThh:mm:ssTZD

where:

YYYY	four-digit year
ΜΜ	two-digit month (01=January, etc.)
DD	two-digit day of month (01 through 31)
hh	two digits of hour (00 through 23) (am/pm NOT allowed)
mm	two digits of minute (00 through 59)
ss	digits of second (00 through 59)
TZD	time zone designator

Time zone designators:  

Z	indicates UTC (Coordinated Universal Time). The "Z" must be uppercase.
+hh:mm	indicates that the time is a local time which is hh hours and mm minutes ahead of UTC.
-hh:mm	indicates that the time is a local time which is hh hours and mm minutes behind of UTC.

Exactly the components shown here must be present, with exactly this punctuation. Note that the "T" letter appears literally in the string (it must be uppercase), to indicate the beginning of the time element, as specified in [ISO8601]

If a generating application does not know the time to the second, it may use the value "00" for seconds (and minutes and hours, if necessary).

Note. [Datetime] does not address the issue of leap seconds.