8.2.4 Implicit Alignment for Muliple Analyses Analyses may be aligned implicitly by treating the running text as a simple series of units, each unit containing one or more levels of content. Typically the levels of content are a base form and any number of annotations of that base form; the contents of the unit at a given level will typically be either a simple text string or a series of (nested) units at the next lower level of analysis. Annotation levels can attach either to the base or to another annotation level. Each level of content may optionally be described with a type attribute which describes what type of analysis it contains. This attribute can be any text string; typical values would include original transcription, retranscription, word-by-word gloss, allomorphic transcription (i.e. a transcription which indicates morpheme boundaries as cuts within the surface form of a word), morphemic representation, and so on.Compare the discussion of parallel texts in chapter 6. The unit structure could be used for parallel texts; the values of type might in that case be sigla for the various versions of the text. Like all other tags, both unit and level may have an ID attribute which assigns a unique identifier to the element. Optionally, any level of annotation may point with a base attribute to the level of content on which it is based.E.g. a morphemic-representation level might point at the allomorphic representation level, which in turn points at the orthographic level. This definition of annotated unit is kept intentionally general. Every individual analyst is likely to want to use a different scheme of analysis, involving different kinds of units and involving different sets of annotations (likely to include completely novel annotations) even when the same kinds of units are used. In view of this the proposed markup scheme makes no commitment to any of the content of the analysis. The type attribute is provided to allow the user to encode information about the semantic structure of the analysis. Application software could use the type values to process the analyzed data in accordance with that semantic structure. For instance, an editor might use the type of a unit to constrain the types and relative order of its annotations. A formatter could use the annotation types to select font parameters; it would use unit types to select interlinear alignment (for the annotations of low-level units) versus synchronization in parallel columns (for the annotations of high-level units). The SGML declarations required for the elements described here is: Strictly speaking, of course, it is desirable to allow all the phrase-level tags described elsewhere in these guidelines to appear within units and levels; the formal document type declarations in the appendix allow anything to occur within a level element which can occur within a paragraph. Work needs to be done to ensure that the LEVEL and UNIT elements and the TYPE attribute are readily translatable into feature structures and alignment maps. -Ed.