[Código Javascript] Aumentar y disminuir texto

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<a href="javascript:ts('body',2)">Aumentar</a>
<a href="javascript:ts('body',-1)">Dismunuir</a>

<a href="javascript:ts('body',2)"><img src="Url de imagen de aumentar"/></a>
<a href="javascript:ts('body',-1)"><img src="Url de imagen de disminuir"/></a>