Regex quirk of the Playground

Apologies if this is a naive question, but I've been having some difficulty
with the shacl sh:pattern operator; I was working on a rule to allow the
various types for schema:ImageObject width and height values and had tried
the following property rules in my shape:

    sh:property [
        sh:path schema:width ;
        sh:or (
            [ sh:class schema:QuantitativeValue ]
            [ sh:datatype xsd:integer ]
            [ sh:datatype xsd:string ;
                sh:pattern "^\\d+\\.?\\d*.*" ]
            ) ;
        ] ;
    ] .

Then using this test data:
ex:BobsPix
  a schema:ImageObject ;
  schema:url "http://bob.pmx" ;
  schema:height "600"^^xsd:string;
  schema:width "600 ft"^^xsd:string ;
.

In shacl.org/playground, this fails to match the string "600" (with or
without the ^^xsd:string); it will match the string "600.0" and if I
replace the '?' with '*' it will accept "600", but then also accepts
"600..0".

Neither version accepts "600 px" or even "600.0 px" which I had expected to
be covered with the trailing ".*"

is this a quirk of the playground, or are the shacl pattern rules
restricted to a subset of regex syntax?

Both the question operator and ".*" seem to be supported in
https://www.w3.org/TR/xpath-functions/#regex-syntax (.* is used in the
examples) -- is there something else that I'm missing? (my tests work fine
in https://regex101.com/ :)

any and all guidance greatly welcomed ;)

-- 
Gary Lawrence Murphy <gary@schemaapp.com> - Hunch Manifest, 15 Wyndham N
'C', Guelph