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: Generally , carboplatin is said to have milder side effects than cisplatin , whose ocular and orbital toxicity are well known .
### Output Text:
Generally , <span class="chemical">carboplatin</span> is said to have milder side effects than <span class="chemical">cisplatin</span> , whose ocular and orbital toxicity are well known . 