In the sentence extracted from biomedical literature, identify all the chemical entities. The required answer format is the same sentence with HTML <span> tags to mark up specific entities. 
### Entity Markup Guides:
Use <span class="chemical"> to denote a chemical.

### Input Text: WHAT THE READER WILL GAIN : The reader will gain better insight into the safety of capecitabine in special populations such as patients with advanced age , renal and kidney disease .
### Output Text:
WHAT THE READER WILL GAIN : The reader will gain better insight into the safety of <span class="chemical">capecitabine</span> in special populations such as patients with advanced age , renal and kidney disease . 