Self-Admitted Technical Debt (SATD) represents the admission, made through source code comments or other channels, of portions of a program being poorly implemented, containing provisional solutions or, in general, simply being not ready yet. To better understand developers’ habits in SATD annotation, and possibly support their exploitation in tool support, this paper provides an in-depth analysis of the content provided in SATD comments, and the expressed sentiment. We manually inspect and classify 1038 instances from an existing dataset, grouping them along a taxonomy composed of 41 categories (of which 9 top-level ones), identifying their sentiment, and the presence of external references such as author names or issue IDs. Results of our study indicate that (i) the SATD content is crosscutting along life-cycle dimensions identified in previous work, (ii) comments related to functional problems or on-hold SATD are generally more negative than poor implementation choices or partially implemented functionality, and (iii) despite observations from previous literature, only a minority of SATD comments leverage external references.