The segment over which an element extends is in some cases called the DOMAIN or interval or length of the element. […] In the course of analysis it is usually more convenient not to set up absolute divisions, e.g. word and phrase, and then say that various relations cross these divisions (e.g. syllabification rules cross word division in Hungarian but not in English). Instead, the domain of each element,or each relation among elements, is indicated when the element in question is set up. If many of these domains appear to be equivalent, as is frequently the case, that fact may then be noted and we may define a domain such as WORD or the like.
- Harris (1951), a pag.15, n.15

The succession of unit segments over which a component is defined may be called its extension ( or domain, or scope ).
- Harris (1951), a pag.130

[…] one of the conveniences of setting up the domains of sequence resultants, components, and constructions is that it is these domains which usually correlate with the point of occurrence of these intermittently present elements. We can group together all sequence resultants, components, and constructions whose domains involve the same boundary junctures, intermittently present phonologic elements, contours, or other features. The juncture, contour, or other feature involved would then be said to apply to the domain common to all these, or to the class of morphological elements (and sequences) which includes all these. In many languages we will find several such sets of features, marking several types of domains (usually one enclosing the other).
- Harris (1951), a pag.345

In many languages there are phonemic or phonetic features which extend over the length of various morphological domains. E.g. in English and in other languages, the constructions which sometimes occur by themselves ('FB': a free morpheme with zero or more bound forms, occasionally doubled or trebled with ˏˏ stress) have exactly one loud stress; and in general no stretch of speech contains precisely one loud stress except one of these. A domain of this type is often called a word. There may be several contrasting construction types all having the same contour (and boundary) features, and hence constituting the same domain. This, or a somewhat similar domain may also be the domain of other and less frequently noticed features. E.g. in some languages, the duration of phonemes is longer if the word in which they are contained is shorter. The phonemes /tæb/ are longer in 'The number on this tab has to be registered' than in 'The number on this tabulating-machine has to be registered'. If we find, for example, that the domain of vowel harmony in a language is somewhat larger than the domain of word-tone contours, or that its effect carries for one morpheme class in the sequence longer than do the morphophonemic changes of tone, we merely recognize two domains, one being that of tone contours and the other, including or overlapping it, being that domain of vowel harmony. Both would roughly be the length and character of what is often called the word.
- Harris (1951), a pag.345

An important factor in the compact statement of relation among elements is the specification of the domain over which the relation occurs. Within the domain, we state not only the occurring together or the substitution of elements but also their relative order, and any variation in these which depends upon the other environment.
- Harris (1951), a pag.369, n.11