Any week during the whole or part of which an employee's relations with his employer are governed by a contract of employment counts in computing the employee's period of employment.
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Subject to subsection (4), any week (not within subsection (1)) during the whole or part of which an employee is—
incapable of work in consequence of sickness or injury,
absent from work on account of a temporary cessation of work, or
absent from work in circumstances such that, by arrangement or custom, he is regarded as continuing in the employment of his employer for any purpose, . . .
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counts in computing the employee's period of employment.
Not more than twenty-six weeks count under subsection (3)(a) . . . between any periods falling under subsection (1).