This appendix is normative.
The following are notes about implementation requirements corresponding to various features in the SVG language.
Conforming SVG User Agents user agents must treat unknown
attributes, attribute values, styling properties, styling property
values, and descendant elements as follows:
Since 'fill' is an inherited property, and since the 'fill' attribute on the 'circle' element is ignored due to the above rules, the circle's fill is indeed green, and not black.
<g fill="green"> <circle fill="hey baby, like wow" r="50"/> </g>
When unsupported content is encountered, an SVG user agent which provides access to an error console should report the incidence of unsupported content, the location where it was encountered, and other appropriate messages that may help the author, to the error console.
A conforming SVG User Agent user agent must process errors in the
following manner.
There are various scenarios where an SVG document fragment must be considered technically in error :
A document can go in and out of error over time. For example, document changes from the SVG uDOM or from animation can cause a document to become in error and a further change can cause the document to become correct again.
When a document is in error the SVG
User Agent user
agent must provide a highly perceivable indication
of error. Additionally, an SVG user agent
which provides access to an error console should report the error,
the location where it was encountered, and other appropriate
messages that may help the author, to the error console.
Because of situations where a block of scripting changes might cause a given SVG document fragment to go into and out of error, error processing shall occur only at times when document presentation (e.g., rendering to the display device) is updated.
User
Agents agents must only consider elements
explicitly placed in the SVG namespace by XML Namespace
declarations in the document (e.g., <svg
xmlns="http://www.w3.org/2000/svg">) as being SVG elements.
SVG content can use attributes 'requiredFeatures' and 'requiredExtensions' to provide explicit
indication of the minimal features that must be supported by the
SVG
User Agent user
agent in order to render the SVG content
correctly. SVG content can also use attributes 'version' in conjunction with 'baseProfile' to provide explicit indication
of the minimal features that must be supported. For example, if
'version' is 1.2 and 'baseProfile' is tiny , then these attributes indicate that the
content requires a SVG
User Agent user
agent that minimally supports the SVG Tiny 1.2
specification. If an SVG
User Agent user
agent does not support the minimal required
feature set, then the user agent should alert or otherwise provide
a highly visible notification to the user that it may not be able
to render the content correctly.
However, SVG content that provides a specified value for 'version' but does not provide a specified value for 'baseProfile' simply indicates to the user agent the specification level (1.0, 1.1, 1.2) to which the content conforms. If 'version' is specified but not 'baseProfile' , the SVG content does not provide sufficient information to the user agent to determine the minimum feature set that is required to render the content; the user agent can only know that the author might be using SVG language features that were not defined in earlier versions of the language. Therefore, if the SVG content specifies a version of the SVG language unknown to the user agent, then the user agent should alert or otherwise provide a highly perceivable notification to the user that it may not be able to render the content correctly.
When SVG content specifies SVG language versions, profiles,
features or extensions not supported by the currently installed
user agent, the user agent may notify the user how to update the
SVG
User Agent user
agent should a newer version be available which
does support these features.
Note that the intent of the version number is to indicate the minimum implementation version for the content; an SVG user agent which encounters content with a version number unknown to the user agent must still render those elements and attributes that it does support, and must not render elements or document fragments with root elements which it does not support.
This section describes the behaviour of SVG
User Agents user
agents .
Some numeric attribute and property values have restricted ranges, such as color component values. When out-of-range color or opacity values are provided, the user agent should defer any error checking until after presentation time, as composited actions might produce intermediate values which are out-of-range but final values which are within range.
Color values are not in error if they are out-of-range, even if
final computations produce an out-of-range color value at
presentation time. User agents should clamp color values to the
nearest color value (possibly determined by simple clipping) which
the system should process as late as possible (e.g., presentation
time), although it is acceptable for SVG
User Agents user
agents to clamp color values as early as parse
time. Thus, implementation dependencies might preclude consistent
behavior across different systems when out-of-range color values
are used.
Opacity values out-of-range are not in error and should be clamped to the range 0 to 1 at the time which opacity values have to be processed (e.g., at presentation time or when it is necessary to perform intermediate filter effect calculations).
A conforming SVG User Agent user agent must implement path
rendering as follows:
(newx1, newy1) = (curx - (oldx2 - curx), cury - (oldy2 - cury)) = (2*curx - oldx2, 2*cury - oldy2)
This specification does not mandate any particular scheme for
visual feedback for text selection, but a conforming SVG
User Agent user
agent should provide such feedback as is consistent with
system norms.
The following implementation notes describe the algorithm that
must be used for deciding which characters are selected during a
text selection operation. A
conforming SVG User Agent user agent must implement the behaviour specified
by this algorithm.
As the text selection operation occurs (e.g., while the user clicks and drags the mouse to identify the selection), the user agent determines a start selection position and an end selection position , each of which represents a position in the text string between two characters. After determining start selection position and end selection position, the user agent selects the appropriate characters, where the resulting text selection must consist of either:
On systems with pointer devices, to determine the start
selection position , the SVG
User Agent user
agent should determine which boundary between
characters corresponding to rendered glyphs is the best target
(e.g., closest) based on the current pointer location at the time
of the event that initiates the selection operation (e.g., the
mouse down event). The user agent should then track the completion
of the selection operation (e.g., the mouse drag, followed
ultimately by the mouse up). At the end of the selection operation,
the user agent should determine which boundary between characters
is the best target (e.g., closest) for the end selection
position .
If no character reordering has occurred due to bidirectionality, then the selection must consist of all characters between the start selection position and end selection position . For example, if a 'text' element contains the string "abcdef" and the start selection position and end selection positions are 0 and 3 respectively (assuming the left side of the "a" is position zero), then the selection shall consist of "abc".
When the user agent is implementing selection of bidirectional text, and when the selection starts (or ends) between characters which are not contiguous in logical order, then there may be multiple potential combinations of characters that can be considered part of the selection. The algorithms to choose among the combinations of potential selection options shall choose the selection option which most closely matches the text string's visual rendering order.
When multiple characters map inseparably to a given set of one
or more glyphs, the user agent may either disallow the selection to
start in the middle of the glyph set or may attempt to allocate
portions of the area taken up by the glyph set to the characters
that correspond to the glyph. For systems
which support selection, the user agent must provide a mechanism
for selecting text with a full range of available UI devices (e.g.
keyboard, mouse, pen, or any other pointer device) as a default,
even when the given text is part of a link. One implementation
option for platforms which support selection via a pointer device
such as a mouse is for the user agent to provide for a small
additional region around character cells which initiates text
selection operations but does not initiate event handlers or links.
Additionally, the user agent must allow scripted or programmatic
DOM access to all text content, and specifically any selected or
focused content, at all times. C.8 Printing implementation notes
Conforming SVG User Agents which support both zooming on display
devices and printing, the default printing option should produce
printed output that reflects the display device's current view of
the current SVG document fragment (assuming there is no
media-specific styling), taking into account any zooming and
panni