1. Personal Needs and Preferences Properties

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User preferences are defined to support web authors in delivering a best-fit match from resources available to a person's needs expressed in terms of modalities the user can receive. Not all content can readily meet a user's needs in every context but where preferences are available a better match might be made than where they are not. Matching a user's explicitly-expressed needs might require changing configurations on a delivery device, reporting to a web app what those preferences are and adaptations the device has made  to them and the web app may itself change configuration and may fetch and deliver alternative content to meet the needs.

In some cases a preference might be addressed directly and completely by a device. In some cases a device may partially address a preference and further support for that preference will need to be provided by a web app and in some cases the web app will address the preference.  This is likely to be different for each preference, device, environmental and other context.

1.1 Processing of Preferences

In this section we present an example as an introduction, ahead of its full definition.

This specification provides a number of Preference Property Definitions expressed in terms of sensory modalities and recognised adaptation types.  Each preference property instance consists of a (space-separated unordered) list of tokens taken from a strict vocabulary for that property.  For example the preference 

textualForAuditory

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indicates a user wishes auditory resources to be replaced by or augmented by textual resources.  This may be done in different ways depending on the media context.  Its values are a list drawn from the vocabulary:

Token Values	Description
true	A preference that audio modalities are replaced or augmented by textual ones
false	Default value - no preference
captions	A preference that captions be delivered simultaneously with the audio
transcript	A preference that video be replaced by a transcript.
transcript-simultaneous	A preference that a transcript be delivered at the same time as audio or video

If the property has a value of '(true)' this is to be interpreted as a general requirement and a textual form delivered that is appropriate for the media concerned drawn from other tokens in that vocabulary as appropriate to the media context.  A value of (captions)  or (true captions) is to be interpreted as that the user wishes for audio to be accompanied by captions. It implies that the property is true and an intelligent system might infer that if captions are not available but a transcript is then this might be useful to deliver instead even though the user has not requested it explicitly.  The token 'false' must occur alone so a list of tokens containing 'false" and any other value is undefined (this includes '(true false)'.  The application should provide the best match to the user's preferences.

1.2 Organisation of Preference Properties

Properties are described in terms of the modalities to which they relate. There are two kinds:

• Properties that relate to delivery of a specific modality - for example highContrast relates to a visual modality.
• Properties that relate a preferred modality to an existing one and optionally give specific adaptation types that are preferred.

An instance of a property consists of a (space separated, unordered) list of tokens drawn from a vocabulary for that property.

Where a property preference is for one modality over another delivery may be augmenting the one modality with another or replacing it depending on the best match to the user's context, which may be determinable from other preference settings. For example a user may specify that they prefer auditory information be delivered in textual form with the setting

A textual alternative might be delivered to the user instead of the audio or displayed simultaneously with rendering the audio. Note that some users find considerable benefit from simultaneous rendering of resources in multiple modalities, particularly but not exclusively users with particular cognitive disabilities, non-native language speakers and language learners.  The choice of whether to render the text simultaneously with the audio might be made by matching also to a user's language preferences or by the context of the media possibilities.
Each property instance has a value that consists of a list of tokens as specified in the definition of properties. Each token has an optional list of refinement parameters where such is meaningful.

1.2.1 Interpretation of values

[Editors note: This needs a little careful work to tighten it - for example for some vocabulary (true false X Y) is the instance (true) equivalent to (X Y) ? ]

Lists of values may not be logically inconsistent. In particular the following are prohibited and if they occur are undefined:

• Any list of values containing both true and false
• Any list of values containing false together with any other value (i.e. false must occur alone)
• A list of values consisting of (true X) should be considered equivalent to (X)

Where a list of values contains true and any other values the other values should be considered as refining the value true (i.e. providing more detail of what is preferred). A system responding to the value for some property of

might make intelligent inferences about media that might be useable by that user in that context.  Where a vocabulary contains terms (true, false, X, Y) and an instance of a property is either (true, X) or just (X) a system would ideally deliver an X if it is available but if an X is not available then the system might infer that a Y would be useful and deliver that instead.

1.3 Preference Property Definitions

1.3.1 auditory

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Indicates a preference for auditory resources

Token Values	Description
true	Prefer auditory resources
false	Default value - no preference

Examples:

1.3.2 textual

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Indicates a preference for textual resources

Token Values	Description
true	Prefer textual resources
false	Default value - no preference

Examples:

1.3.3 visual

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Indicates a preference for visual resources

Token Values	Description
true	Prefer visual resources
false	Default value - no preference
highContrast	Where visual is the preferred modality the preference is for presentation of text and images of text that has a contrast ratio of at least 4.5:1, or, for larger text, a contrast ratio of at least 3:1 (WCAG2 Checkpoint 1.4.3): http://www.w3.org/TR/WCAG20/#visual-audio-contrast.
blackOnWhite	black text and borders on a white background
whiteOnBlack	white text and borders on a black background
inverseVideo	Text, image and video colors reversed

Examples:

1.3.4 tactile

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Indicates a preference for tactile resources

Token Values	Description
true	Prefer tactile resources
false	Default value - no preference

Examples:

1.3.5 textualForAuditory

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Indicates a preference that an auditory resource or presentation be augmented by or replaced by a textual one

Token Values	Description
true	A preference that audio modalities are replaced or augmented by textual ones
false	Default value - no preference
captions	A preference that captions be delivered simultaneously with the audio
transcript	A preference that video be replaced by a transcript.
transcript-simultaneous	A preference that a transcript be delivered at the same time as audio or video

Examples:

1.3.6 textualForVisual

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Indicates a preference that a visual resource or presentation be augmented by or replaced by a textual one

Token Values	Description
true	A preference that visual modalities are replaced or augmented by textual ones
false	Default value - no preference
alternativeText	A preference for alternative text instead of or together with a resource wth visual modality (typically an image)
longDescription	A preference that a visual modality resource be replaced by or augmented by a longDesc.

Examples:

1.3.7 textualForTactile

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Indicates a preference that a tactile resource or presentation be augmented by or replaced by a textual one

Token Values	Description
true	A preference that tactile modalities are replaced or augmented by textual ones
false	Default value - no preference

Examples:

1.3.8 visualForAuditory

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Indicates a preference that an auditory resource or presentation be augmented by or replaced by a visual one

Token Values	Description
true	A preference that auditory modalities are replaced or augmented by visual ones
false	Default value - no preference
signLanguage	A preference that an auditory resource be replaced by or augmented by a sign language presentation, as defined above [TBD url to defin]

Examples:

1.3.9 visualForTactile

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Indicates a preference that a tactile resource or presentation be augmented by or replaced by a visual one

Token Values	Description
true	A preference that tactile modalities are replaced or augmented by visual ones
false	Default value - no preference

Examples:

1.3.10 visualForTextual

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Indicates a preference that a textual resource or presentation be augmented by or replaced by a visual one

Token Values	Description
true	A preference that textual modalities are replaced or augmented by visual ones
false	Default value - no preference

Examples:

1.3.11 auditoryForVisual

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Indicates a preference that an visual resource or presentation be augmented by or replaced by an auditory one

Token Values	Description
true	A preference that visual modalities are replaced or augmented by auditory ones
false	Default value - no preference
audioDescription	A preference that a visual resource (typically the visual component of a video) be replaced by or augmented by an audio description. Note that in some countries this is referred to as 'videoDescription'.

Examples:

1.3.12 auditoryForTactile

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Indicates a preference that a tactile resource or presentation be augmented by or replaced by an auditory one

Token Values	Description
true	A preference that tactile modalities are replaced or augmented by auditory ones
false	Default value - no preference

Examples:

1.3.13 auditoryForTextual

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Indicates a preference that a textual resource or presentation be augmented by or replaced by an auditory one

Token Values	Description
true	A preference that textual modalities are replaced or augmented by auditory ones
false	Default value - no preference

Examples:

1.3.14 tactileForAuditory

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Indicates a preference that an auditory resource or presentation be augmented by or replaced by an tactile one

Token Values	Description
true	A preference that auditory modalities are replaced or augmented by tactile ones
false	Default value - no preference

Examples:

1.3.15 tactileForVisual

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Indicates a preference that a visual resource or presentation be augmented by or replaced by a tactile one

Token Values	Description
true	A preference that visual modalities are replaced or augmented by tactile ones
false	Default value - no preference

Examples:

1.3.16 tactileForTextual

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Indicates a preference that a textual resource or presentation be augmented by or replaced by a tactile one

Token Values	Description
true	A preference that textual modalities are replaced or augmented by tactile ones
false	Default value - no preference

Examples:

1.3.17 languageOfAdaptation

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Indicates a preference for adaptations to be delivered in a particular language. Note that this may not be the same language in which the user operates the device.

Token Values	Description
Internal Language Code presented to user as string or selectable widget	TBD: get IETF reference
undefined	Preference is for adaptations to be delivered in the default user language for that device

Examples:

1.3.18 hazard

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Indicates characteristics of resources that a user DOES NOT wish to receive because of potential hazards for that user. Note also that the meaning of a value of true without any other value is undefined for this property (i.e. it must have a refinement to be meaningful)

Token Values	Description
false	Default value - no preference
flashing	A preference that a resource having a visual pattern that flashes more than three times in any one second not be delivered to the user. Note that this level of flashing can cause seizures in some users (WCAG2 Guideline 2.3.1 A): http://www.w3.org/TR/WCAG20/#seizure].
flashingStrict	A preference that a resource having a visual pattern that flashes more than three times in any one second not be delivered to the user. Note that this level of flashing can cause seizures in some users (WCAG2 Guideline 2.3.1 AAA):  http://www.w3.org/TR/WCAG20/#seizure
motionSimulation	A preference that a resource simulating motion not be delivered to the user. Note that for some users such a resource may induce nausea
sound	Prefer that resources generating an audio pattern that can cause the user to have seizures [ISO 29138] not be delivered to the user.

Examples:

1.3.19 ATInteroperable

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Indicates that where possible resources that are interoperable with AT should be selected. Note that the default for this preference unless otherwise defined is true.

Token Values	Description
true (default)	Resources that are interoperable with AT should be selected whenever possible. Interoperability is indicated by compliance with WCAG 2.0 checkpoints: 1.1.1, 1.3.1, 1.3.2, 2.4.4, 3.1.1, 3.1.2, 3.3.2, 4.1.1 and 4.1.2.
false	explicit preference excluding this requirement

Examples:

1.3.20 simplePresentation

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Indicates a preference for very simple presentation of interface and content even if the device supports more complex presentation (for example if the device large or high-resolution screen)

Token Values	Description
true	A preference for presentation to be of a similar level of complexity to that commonly delivered to small screen devices using agile design - typically no more than six controls or regions of interest on a page.
false	Default value - no preference