HTML has parsing algorithms at https://html.spec.whatwg.org/multipage/common-microsyntaxes.html#numbers that amount to "trim any leading TAB/LF/FF/CR/SPACE sequence and use the longest valid remaining prefix". But HTTP structured field value parsing is much more strict and amounts to requiring Integer input to match regular expression pattern ^-?[0-9]{1,15}$; see https://www.rfc-editor.org/rfc/rfc8941#name-parsing-structured-fields and subsections for Item and Integer/Decimal.

For generation, there's step 16 of https://html.spec.whatwg.org/multipage/common-microsyntaxes.html#rules-for-parsing-floating-point-number-values , step 7 of https://webidl.spec.whatwg.org/#abstract-opdef-converttoint , https://html.spec.whatwg.org/#number-state-(type=number) , https://html.spec.whatwg.org/#cropped-to-the-source-rectangle-with-formatting , and https://html.spec.whatwg.org/#create-a-date-object .