[selectors] Spelling and grammar mistakes

There are a bunch of spelling and grammar mistakes within the Selectors
Level 4 spec. The following lists them including the correction after the
=> arrow.

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E:lang(zh, "*-hant")     an element of type E tagged as being either in
Chinese (any dialect or writing system) or othewise written with
traditional Chinese characters => otherwise

E:drop     an E element that can possibly receieve a drop => receive

tagname => tag name

The DOM document structure is powerful and useful, but generic enough to
model pretty much any langauge that describes tree-based data (or even
graph-based, with a suitable interpretation). => language

etc => etc.

As usual for CSS syntax, white space is allowed arond the arguments between
the parentheses of a functional pseudo-class, unless otherwise specified.
=> around

Selectors provides the pseudo-classes :link and :visited to distinguish
them: => provide

namespace prefixes are declared with the @namespacerule. => missing space
after @namespace

This corresponds to the behaviour of non-validating processors as defined
by the XML specification. => behavior (in case US English should be used in
specs)

This is is a (potentially empty) set of elements => double 'is'

Additionaly, the parent of an element that matches :focus-within also
matches :focus-within. => Additionally

Selectors introduces the concept of structural pseudo-classes => introduce

For example, the following element matches :blank, but not :empty, because
it contains at least one linebreak, and possibly other whitespace: => line
break

if all the values are tied, the two specifities are equal. => specificities

Literal strings correspond to delim tokens with the given value. =>
delimiter

(See :matches()for examples.) => missing space after :matches()

testcases => test cases

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Note that I am not a native English speaker. So there might be some
mistakes I've missed.

Best regards,

Sebastian