Table of Contents

• 1. Introduction
• 2. Conformance
• 3. Terminology
• 4. Frame Timing
  • 4.1 Introduction
  • 4.2 Extensions to the Performance Interface
    • 4.2.1 Attributes
    • 4.2.2 Methods
  • 4.3 The PerformanceRenderTiming Interface
    • 4.3.1 Attributes
  • 4.4 The PerformanceCompositeTiming Interface
    • 4.4.1 Attributes
• 5. Monotonic Clock
• 6. Privacy and Security
• A. Acknowledgements
• B. References
  • B.1 Normative references
  • B.2 Informative references

2. Conformance

As well as sections marked as non-normative, all authoring guidelines, diagrams, examples, and notes in this specification are non-normative. Everything else in this specification is normative.

The key words MAY, MUST, and SHOULD are to be interpreted as described in [RFC2119].

Requirements phrased in the imperative as part of algorithms (such as "strip any leading space characters" or "return false and abort these steps") are to be interpreted with the meaning of the key word ("MUST", "SHOULD", "MAY", etc) used in introducing the algorithm.

Some conformance requirements are phrased as requirements on attributes, methods or objects. Such requirements are to be interpreted as requirements on user agents.

Conformance requirements phrased as algorithms or specific steps may be implemented in any manner, so long as the end result is equivalent. (In particular, the algorithms defined in this specification are intended to be easy to follow, and not intended to be performant.)

The IDL fragments in this specification MUST be interpreted as required for conforming IDL fragments, as described in the Web IDL specification. [WebIDL]

3. Terminology

The construction "a Foo object", where Foo is actually an interface, is sometimes used instead of the more accurate "an object implementing the interface Foo".

The term "JavaScript" is used to refer to ECMAScript [ECMA-262], rather than the official term ECMAScript, since the term JavaScript is more widely known.

4. Frame Timing

partial interface Performance {
    void clearFrameTimings ();
    void setFrameTimingBufferSize (unsigned long maxSize);
                attribute EventHandler onframetimingbufferfull;
};

interface PerformanceRenderTiming : PerformanceEntry {
    readonly    attribute unsigned long sourceFrameNumber;
};

interface PerformanceCompositeTiming : PerformanceEntry {
    readonly    attribute unsigned long sourceFrameNumber;
};

5. Monotonic Clock

The time values stored within the interface MUST monotonically increase to ensure they are not affected by adjustments to the system clock. The difference between any two chronologically recorded time values MUST never be negative. The user agent MUST record the system clock at the beginning of the navigation and define subsequent time values in terms of a monotonic clock measuring time elapsed from the beginning of the navigation.