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Headers constructor
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Accept: before-æøå-after
X-Test: before-ß-after

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Headers.append()
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Accept: before-æøå-after
X-Test: before-ß-after

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Headers.set()
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Accept: before-æøå-after
X-Test: before-ß-after

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Headers.getSetCookie()
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Set-Cookie: before-æøå-after

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Headers iterator
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accept: before-æøå-after
x-test: before-ß-after

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Headers.forEach()
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accept: before-æøå-after
x-test: before-ß-after
