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Content for  TR 21.801  Word version:  16.2.0

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E (Normative)  Verbal forms for the expression of provisionsWord‑p. 41
The verbal forms shown in table E.1 shall be used to indicate requirements strictly to be followed in order to conform to the standard and from which no deviation is permitted.
Verbal form
Equivalent expressions for use in exceptional cases (see clause 6.6.1)

shall
is to
is required to
it is required that
has to
only ... is permitted
it is necessary
shall not
is not allowed [permitted] [acceptable] [permissible]
is required to be not
is required that ... be not
is not to be

Do not use "must" as an alternative for "shall". (This will avoid any confusion between the requirements of a standard and external statutory obligations).
Do not use "may not" instead "shall not" to express a prohibition.
To express a direct instruction, for example referring to steps to be taken in a test method, use the imperative mood (e.g. "switch on the recorder").
The verbal forms shown in table E.2 shall be used to indicate that among several possibilities one is recommended as particularly suitable, without mentioning or excluding others, or that a certain course of action is preferred but not necessarily required, or that (in the negative form) a certain possibility or course of action is deprecated but not prohibited.
Verbal form
Equivalent expressions for use in exceptional cases (see clause 6.6.1)

should
it is recommended that
ought to
should not
it is not recommended that
ought not to

The verbal forms shown in table E.3 are used to indicate a course of action permissible within the limits of the 3GPP TS or 3GPP TR.
Verbal form
Equivalent expressions for use in exceptional cases (see clause 6.6.1)

may
is permitted
is allowed
is permissible
need not
it is not required that
no ... is required

Do not use "possible" or "impossible" in this context.
Do not use "can" instead of "may" in this context.
Do not use "may" or "may not" to indicate a possibility or lack of possibility - see Table E.4 below.
NOTE:
"May" signifies permission expressed by the standard, whereas "can" refers to the ability of a user of the standard or to a possibility open to him.

The verbal forms shown in table E.4 are used for statements of possibility and capability, whether material, physical or causal.
Verbal form
Equivalent expressions for use in exceptional cases (see clause 6.6.1)

can
be able to
there is a possibility of
it is possible to
cannot
be unable to
there is no possibility of
it is not possible to

Do not use "may" instead of "can" in this context. Do not use "may not" in this context.
NOTE:
"May" signifies permission expressed by the standard, whereas "can" refers to the ability of a user of the standard or to a possibility open to him. If there is uncertainty about whether an event will or will not happen, in particular where the normally expected behaviour will sometimes be impossible, a formulation such as "cannot always" should be used.

The verbal forms shown in table E.5 shall be used to indicate behaviour of equipment or sub-systems outside the scope of the document in which they appear. For example, in a standard specifying the requirements of terminal equipment, these forms shall be used to describe the expected behaviour of the network or network simulator to which the terminal is connected.
Verbal form
Equivalent expressions

will
will not

Distinguish from "shall" / "shall not". Use to express behaviour of equipment or systems outside the scope of the document being drafted, where description of such behaviour is essential to the correct understanding of the requirements pertaining to equipment within the scope of the current document.
EXAMPLE:
Extract from standard specifying behaviour of terminal equipment: "… On expiry of timer T3, the terminal shall send a TIMEOUT message to the network and start timer T4. The network will respond with a TIMOUT-ACKNOWLEDGE message. On receipt of a TIMEOUT-ACKNOWLEDGE message, the terminal shall stop timer T4 …"; thus is distinguished the strong future ("the terminal shall") used for requirements and the normal future ("the network will") used to indicate expected events.
The verbal forms shown in table E.6 shall be used to indicate statements of fact.
Verbal form
Equivalent expressions

is
Any verb in the indicative mood, present tense.
is not

Distinguish from "shall" / "shall not". Do not use present indicative of verbs for expressing requirements.
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F  Checklist concerning quantities and units to be used in 3GPP TSs or 3GPP TRsWord‑p. 44
Void.

G  Example layout of a typescript

Void.

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