Interlinear gloss

In linguistics and pedagogy, an interlinear gloss is a gloss (series of brief explanations, such as definitions or pronunciations) placed between lines, such as between a line of original text and its translation into another language. When glossed, each line of the original text acquires one or more lines of transcription known as an interlinear text or interlinear glossed text (IGT)interlinear for short. Such glosses help the reader follow the relationship between the source text and its translation, and the structure of the original language. In its simplest form, an interlinear gloss is simply a literal, word-for-word translation of the source text.
History.
Interlinear glosses have been used for a variety of purposes over a long period of time. One common usage has been to annotate bilingual textbooks for language education. This sort of interlinearization serves to help make the meaning of a source text explicit without attempting to formally model the structural characteristics of the source language.
Such annotations have occasionally been expressed not through interlinear layout, but rather, through enumeration of words in the object and meta language. One such example is Wilhelm von Humboldt's annotation of Classical Nahuatl:
This "inline" style allows examples to be included within the flow of text, and for the word order of the target language to be written in an order which approximates the target language syntax. (In the gloss here, "mache es" is reordered from the corresponding source order to approximate German syntax more naturally.) Even so, this approach requires the readers to "re-align" the correspondences between source and target forms.
More modern 19th- and 20th-century approaches took to glossing vertically, aligning the same sort of word-by-word content in such a way that the metalanguage terms were placed vertically below the source language terms. In this style, the given example might be rendered thus (here English gloss):
Note that here word ordering is determined by the syntax of the object language.
Finally, modern linguists have adopted the practice of using abbreviated grammatical category labels. A 2008 publication which repeats this example labels it as follows:
This approach is denser and also requires effort to read, but it is less reliant on the grammatical structure of the metalanguage for expressing the semantics of the target forms.
In computing, special text markers are provided in the Specials Unicode block to indicate the start and end of interlinear glosses.
Modern implementations.
In recent times, interlinear glossing for language learning has seen a sudden interest. Online companies such as Hyplern have issued a growing online collection of literature classics in multiple languages for learners. The available languages include Latin, Dutch, French, German, Hungarian, Indonesian, Italian, Polish, Portuguese, Russian, Spanish, and Swedish, among others. This breadth of titles resembles what James Hamilton envisioned in the 1800’s. The goal of these new editions is to simplify the effort required to acquire vocabulary while spreading love the world’s greatest literature.
Structure.
A semi-standardized set of parsing conventions and grammatical abbreviations is explained in the Leipzig Glossing Rules.
An interlinear text will commonly consist of some or all of the following, usually in this order, from top to bottom: 
and finally 
As an example, the following Taiwanese clause has been transcribed with five lines of text: 
In linguistics, it has become standard to align the words and to gloss each transcribed morpheme separately. That is, "koat-tēng" in line 1 above would either require a hyphenated two-word gloss, or be transcribed without a hyphen, for example as "koattēng." Grammatical terms are commonly abbreviated and printed in to keep them distinct from translations, especially when they are frequent or important for analysis. Varying levels of analysis may be detailed. For example, in a Lezgian text using standard romanization,
Here every Lezgian morpheme is set off with hyphens and glossed separately. Since many of these are difficult to gloss in English, the roots are translated, but the grammatical suffixes are glossed with three-letter grammatical abbreviations.
The same text may be glossed at a different level of analysis:
Here the Lezgian morphemes are translated into English as much as possible; only those which correspond to English are set off with hyphens.
A more colloquial gloss would be:
Here the gloss is word for word; rather than setting off Lezgian morphemes with hyphens, the English words in the gloss are joined with periods when more than one is required to translate a Lezgian word.
Punctuation.
In interlinear morphological glosses, various forms of punctuation separate the glosses. Typically, the words are aligned with their glosses; within words, a hyphen is used when a boundary is marked in both the text and its gloss, a period when a boundary appears in only one. That is, there should be the same number of words separated with spaces in the text and its gloss, as well as the same number of hyphenated morphemes within a word and its gloss. This is the basic system, and can be applied universally. For example,
An underscore may be used instead of a period, as in "go_out-", when a single word in the source language happens to correspond to a phrase in the glossing language, though a period would still be used for other situations, such as Greek "oikíais" house. 'to the houses'.
However, sometimes finer distinctions may be made. For example, clitics may be separated with a double hyphen (or, for ease of typing, an equal sign) rather than a hyphen:
Affixes which cause discontinuity (infixes, circumfixes, transfixes, etc.) may be set off by angle brackets, and reduplication with tildes, rather than with hyphens:
Morphemes which cannot be easily separated out, such as umlaut, may be marked with a backslash rather than a period:
A few other conventions which are sometimes seen are illustrated in the Leipzig Glossing Rules.