The word boundary is shown by a blank in the L1 text line T. This is repeated in the morphological gloss, and conversely there is a blank in a morphological gloss only if there is a corresponding blank in T.

Rule 13. A word boundary is shown by a blank ( ) both in T and in the gloss line.

Rule 13 prohibits two situations: a word being rendered by a sequence of two words (this is treated in the section on lexemes); and a sequence of two words being rendered by one word.

Occasionally a sequence of two L1 units (words or morphemes) corresponds to one L2 unit. In principle, this situation should not arise in the morphological gloss because each of the L1 units should have its own gloss. However, it is possible that either the L1 units have no meaning in isolation or else mean something totally different than their combination, the latter being idiomaticized. In such cases, glossing them separately might give a misleading impression of the workings of the grammar. When the bisected L1 unit forms an orthographic unit (e.g. a compound), one may simply dispense with the analysis (s. the section on word formation).

If L1 orthography in T requires a blank, the first choice is to gloss the items separately and to leave the semantic interpretation to the idiomatic translation. Then Yucatec Maya le ka'h ‘when’ would be glossed as DEM SR; and Spanish en seguida would be glossed ‘in continuance’.

The second choice is to indicate the semantic unity of the two L1 items typographically by replacing the blank by a boundary symbol that does not interfere with the orthography, e.g. by an underscore: le_ka'h ‘when’; en_seguida ‘immediately’.

If L1 orthography links the two items by another symbol that is also a glossing boundary symbol, as in Engl. vis-à-vis ‘facing’, no satisfactory solution is known.

Rule 14. Two successive orthographic L1 words which are glossed by one L2 word are linked by an underscore (_).