CL-API is an application that generates an API in HTML format, given a package name and reading docstrings.
CL-API documents constanta variables, classes, conditions, functions and macros in different sections.
To generate an API document, you simply call API-GEN function passing the symbol package you want to document and the destination path.
Optionally you might want to excplute some symbol to be documented for a specific section, this is what
:EXCLUDE-CONST :EXCLUDE-VAR :EXCLUDE-CLASS :EXCLUDE-COND :EXCLUDE-FUNC :EXCLUDE-MACRO
API-GEN keys are meant for.
For example to generate CLONSIGNA API, API-GEN was called in the following way: 

(api-gen :clonsigna #P "/tmp/"
         :exclude-func (lambda (s) (or (starts-with "imap" 
                                                     (format nil "~a" s))
                                        (starts-with "bodystructure" 
                                                     (format nil "~a" s))
                                        (starts-with "structure"
                                                     (format nil "~a" s)))))
Optionally you might want to customize the HTML appearence. This is done redefining the *CSS-API* variable.