Judge Juan Merchan plans to issue a ruling tomorrow about the bounds of Donald Trump's cross-examination if the former president decides to testify during the trial.

After hearing a brief oral argument this afternoon, Merchan told the parties he is reserving his decision, which he plans to issue sometime tomorrow.

Prosecutor Matthew Colangelo argued that Trump's alleged prior bad acts as demonstrated by a variety of civil and criminal determinations should be fair game during cross-examination.

The Sandoval hearing on Trump's potential testimony got underway with prosecutors pushing to cross-examine former president Donald Trump about his alleged violation of the limited gag order in his civil fraud trial.

Prosecutor Matthew Colangelo asked Judge Merchan to permit them to ask the former president about his testimony during his civil fraud trial when the former president claimed he was not referring to Judge Arthur Engoron's law clerk during remarks in the hallway of the courthouse last year.

Engoron determined that Trump's brief testimony rang "hollow and untrue."

Colangelo asked Merchan to allow cross-examination about Trump's testimony and the gag order violation last year in order to probe his credibility.

"He lied," Colangelo said of Trump. "It is very hard to think of something more probative of a testifying defendant's credibility."

Judge Juan Merchan began the court's afternoon session but did not mention the self-immolation incident this afternoon in the park across from the courthouse, and Trump did not respond to questions about the incident when asked by a reporter in the hallway outside the courtroom.

The judge plans to hold a Sandoval hearing this afternoon to determine the bounds of Trump's cross-examination if he decides to testify.

In a filing earlier this week, prosecutors said they planned to question the former president about his past civil cases, including $464 million business fraud judgment, the defamation and battery cases brought by E. Jean Carroll and a lawsuit Trump filed against Hillary Clinton claiming she conspired to rig the 2016 election.

Prosecutors also want to question Trump about the Trump Organization's 2022 criminal trial for tax evasion and the civil case against the Trump Foundation for misusing charitable donations to further Trump's political interests.

Trump is seated at counsel table between his lawyers Emil Bove and Todd Blanche. Manhattan District Attorney Alvin Bragg is not present in the courtroom.

Former President Trump has filed a new emergency appeal to change the venue of his criminal trial.

Oral arguments are scheduled for this afternoon to determine whether the trial should be temporarily paused.

The motion is expected to cite some of the responses prospective jurors gave during the jury selection process.

Trump's prior attempts to move the trial out of Manhattan have failed.

Court this morning may start with a hearing over what prosecutors can ask Trump during cross-examination should he take the stand later in the trial.

The judge would hear arguments from both the people and the defense. The proceedings would then move into jury selection later in the morning.

Prosecutors have indicated they would want to cross-examine Trump on approximately "thirteen different court determinations," including the recent civil finding that he sexually abused columnist E. Jean Carroll, the criminal conviction of the Trump Organization last year, the finding that he committed a decade of business fraud, and the dissolution of his charity, according to sources familiar with the matter.

The hearing -- known as a Sandoval hearing -- is standard practice before jury selection and typically occurs when a defendant signals a willingness to testify.

In a filing last month, Trump's lawyers requested a Sandoval hearing to limit the scope of Trump's potential cross examination, if he opted to testify.

ABC News' Katherine Faulders contributed to this report.