The minify function in the htmlmin.main module minifies HTML by removing comments, empty spaces, boolean attributes, optional attribute quotes, and decoding character references, while allowing users to specify areas of HTML that should not be minified, and returns a minified HTML string.
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Here is a Python code template for the `minify` function from the `htmlmin.main` module:

```python
from htmlmin.main import minify

# Define the HTML input
html_input = """
<!-- FOO --> <!--! BAR -->
"""

# Define the parameters
remove_comments = False
remove_empty_space = False
remove_all_empty_space = False
reduce_empty_attributes = True
reduce_boolean_attributes = False
remove_optional_attribute_quotes = True
convert_charrefs = True
keep_pre = False
pre_tags = ('pre', 'textarea')
pre_attr = 'pre'

# Call the minify function
minified_html = minify(
    html_input,
    remove_comments=remove_comments,
    remove_empty_space=remove_empty_space,
    remove_all_empty_space=remove_all_empty_space,
    reduce_empty_attributes=reduce_empty_attributes,
    reduce_boolean_attributes=reduce_boolean_attributes,
    remove_optional_attribute_quotes=remove_optional_attribute_quotes,
    convert_charrefs=convert_charrefs,
    keep_pre=keep_pre,
    pre_tags=pre_tags,
    pre_attr=pre_attr
)

# Print the minified HTML
print(minified_html)
```

You can replace the `html_input` and parameters with your own values. The `minify` function will return a string containing the minified HTML.