| _ | (the underscore) is the placeholder for exactly one character. |
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| % | (the percent sign) is the placeholder for no, one or more than one character. |
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| %% | (two percent signs) is the placeholder for no, one or more than one character, but not for blank space (so that a search ends at word boundaries). |
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At the beginning and at the end, these placeholders are superfluous.
