HTML attributes

Format an attribute dict into an HTML attribute string.

• True renders the bare attribute (disabled); False and None omit the attribute entirely.
• class and style values may use the structured forms; they are normalized here, so merge_attrs output and hand-built dicts render the same. When they normalize to an empty string the attribute is omitted (an empty class="" would read as a boolean attribute under citry's HTML rules).
• Everything else renders key="value", escaped; values with __html__ pass through unescaped.

Example::

format_attrs({"class": ["btn", {"active": True}], "disabled": True, "data-id": 3})
# -> 'class="btn active" disabled data-id="3"'

Merge attribute dicts left to right into one dict.

Every key resolves last-one-wins, except class and style: their values from all dicts are collected and combined per normalize_class / normalize_style, so several sources can contribute classes and style properties without overwriting each other.

Key order in the result is the order each key was first seen, so a later override does not move an attribute.

Example::

merge_attrs(
    {"class": "btn", "id": "first"},
    {"class": {"active": True}, "id": "second"},
)
# -> {"class": "btn active", "id": "second"}

Turn a structured class value into a plain class string.

• A string is used as-is (stripped).
• A dict keeps only the keys whose value is truthy.
• A list may mix strings, dicts, and nested lists. Each item converts to a {class_name: bool} dict (strings split on whitespace, all True) and the dicts merge left to right, so a later falsy entry removes a class added earlier.

Example::

normalize_class(["btn btn-lg", {"active": True, "hidden": False}])
# -> "btn btn-lg active"

Turn a structured style value into an inline CSS string.

• A string is used as-is (stripped).
• A dict renders each entry as property: value;. Property names are used as written (kebab-case); numbers render bare (width: 100).
• A list may mix strings, dicts, and nested lists. Strings are parsed into property dicts (see parse_string_style) and the dicts merge left to right, so the last value of a property wins.

Two special values steer a merge: None skips the entry (an earlier value for the property stands), and a literal False removes the property entirely, even if set earlier.

Example::

normalize_style(["color: red; width: 100px", {"color": "green", "width": False}])
# -> "color: green;"

Parse an inline CSS string into a property dict.

Strips /* ... */ comments. Declarations split on ; except inside parentheses, so url(data:image/png;base64,...) survives. A declaration without a : is dropped.

Example::

parse_string_style("color: red; width: 100px; /* note */")
# -> {"color": "red", "width": "100px"}