Method InsertRule

Used to insert a new rule into the style sheet. The new rule now becomes part of the cascade.

ulong InsertRule(string rule, ulong index)

rule string: The parsable text representing the rule. For rule sets this contains both the selector and the style declaration. For at-rules, this specifies both the at-identifier and the rule content.
index ulong: The index within the style sheet's rule list of the rule before which to insert the specified rule. If the specified index is equal to the length of the style sheet's rule collection, the rule will be added to the end of the style sheet.

ulong: The index within the style sheet's rule collection of the newly inserted rule.

DomException: HIERARCHY_REQUEST_ERR: Raised if the rule cannot be inserted at the specified index e.g. if an @import rule is inserted after a standard rule set or other at-rule.
DomException: INDEX_SIZE_ERR: Raised if the specified index does not correspond to a rule in the style sheet's rule list.
DomException: NO_MODIFICATION_ALLOWED_ERR: Raised if this style sheet is readonly.
DomException: SYNTAX_ERR: Raised if the specified rule has a syntax error and is unparsable.