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: Although the short - term safety ( less than or equal to 6 months ) of danazol has been established in a variety of settings , no information exists as to its long - term safety .
### Output Text:
Although the short - term safety ( less than or equal to 6 months ) of <span class="chemical">danazol</span> has been established in a variety of settings , no information exists as to its long - term safety . 